gcp_compute_instance doesn't add service account to the instance

##### SUMMARY

gcp_compute_instance doesn't apply changes when adding a service account and scopes to and existing (stopped) vm instance

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME

gcp_compute_instance

##### ANSIBLE VERSION

```paste below
ansible 2.9.7
config file = None
ansible python module location = /usr/local/lib/python3.7/site-packages/ansible
executable location = /usr/local/bin/ansible
python version = 3.7.4 (default, Oct 12 2019, 18:55:28) [Clang 11.0.0 (clang-1100.0.33.8)]
```

##### CONFIGURATION

```paste below
ansible-config dump --only-changed -v
No config file found; using defaults
```

##### OS / ENVIRONMENT

```
uname -a
Darwin 18.7.0 Darwin Kernel Version 18.7.0: Tue Aug 20 16:57:14 PDT 2019; root:xnu-4903.271.2~2/RELEASE_X86_64 x86_64
```
##### STEPS TO REPRODUCE

```yaml
- name: Update instance
gcp_compute_instance:
name: "my-test-instance"
zone: us-central1-a
project: my-test-project
auth_kind: serviceaccount
deletion_protection: no
service_account_file: "/Users//Downloads/credentials.json"
service_accounts:
- email: 71752527322-compute@developer.gserviceaccount.com
scopes:
- "https://www.googleapis.com/auth/devstorage.read_only"
- "https://www.googleapis.com/auth/logging.write"
- "https://www.googleapis.com/auth/monitoring.write"
- "https://www.googleapis.com/auth/service.management.readonly"
- "https://www.googleapis.com/auth/servicecontrol"
- "https://www.googleapis.com/auth/trace.append"
status: TERMINATED
state: present
```

##### EXPECTED RESULTS

```json
ok: [localhost] => (item=my-test-instance) => {
"ansible_loop_var": "item",
"canIpForward": false,
"changed": false,
"cpuPlatform": "Unknown CPU Platform",
"creationTimestamp": "2020-04-21T06:11:57.224-07:00",
"deletionProtection": false,
"description": "",
"disks": [
{
"autoDelete": true,
"boot": true,
"deviceName": "my-test-instance",
"diskSizeGb": "10",
"guestOsFeatures": [
{
"type": "VIRTIO_SCSI_MULTIQUEUE"
}
],
"index": 0,
"interface": "SCSI",
"kind": "compute#attachedDisk",
"licenses": [
"https://www.googleapis.com/compute/v1/projects/debian-cloud/global/licenses/debian-9-stretch"
],
"mode": "READ_WRITE",
"source": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a/disks/my-test-instance",
"type": "PERSISTENT"
}
],
"displayDevice": {
"enableDisplay": false
},
"fingerprint": "WY2SwusMoUE=",
"id": "6986067812958818291",
"invocation": {
"module_args": {
"auth_kind": "serviceaccount",
"can_ip_forward": null,
"deletion_protection": false,
"disks": null,
"env_type": null,
"guest_accelerators": null,
"hostname": null,
"labels": null,
"machine_type": null,
"metadata": null,
"min_cpu_platform": null,
"name": "my-test-instance",
"network_interfaces": null,
"project": "my-test-project",
"scheduling": null,
"scopes": [
"https://www.googleapis.com/auth/compute"
],
"service_account_contents": null,
"service_account_email": null,
"service_account_file": "/Users//Downloads/my-test-project-c7549fc3f4db.json",
"service_accounts": [
{
"email": "71752527322-compute@developer.gserviceaccount.com",
"scopes": [
"https://www.googleapis.com/auth/devstorage.read_only",
"https://www.googleapis.com/auth/logging.write",
"https://www.googleapis.com/auth/monitoring.write",
"https://www.googleapis.com/auth/service.management.readonly",
"https://www.googleapis.com/auth/servicecontrol",
"https://www.googleapis.com/auth/trace.append"
]
}
],
"shielded_instance_config": null,
"state": "present",
"status": "TERMINATED",
"tags": null,
"zone": "us-central1-a"
}
},
"item": "my-test-instance",
"kind": "compute#instance",
"labelFingerprint": "42WmSpB8rSM=",
"machineType": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a/machineTypes/f1-micro",
"metadata": {
"ssh-keys": "omissis"
},
"name": "my-test-instance",
"networkInterfaces": [
{
"accessConfigs": [
{
"kind": "compute#accessConfig",
"name": "External NAT",
"networkTier": "PREMIUM",
"type": "ONE_TO_ONE_NAT"
}
],
"fingerprint": "eedH4rIkuwQ=",
"kind": "compute#networkInterface",
"name": "nic0",
"network": "https://www.googleapis.com/compute/v1/projects/my-test-project/global/networks/default",
"networkIP": "10.128.0.8",
"subnetwork": "https://www.googleapis.com/compute/v1/projects/my-test-project/regions/us-central1/subnetworks/default"
}
],
"reservationAffinity": {
"consumeReservationType": "ANY_RESERVATION"
},
"scheduling": {
"automaticRestart": false,
"onHostMaintenance": "TERMINATE",
"preemptible": true
},
"selfLink": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a/instances/my-test-instance",
"serviceAccounts": [
{
"email": "71752527322-compute@developer.gserviceaccount.com",
"scopes": [
"https://www.googleapis.com/auth/devstorage.read_only",
"https://www.googleapis.com/auth/logging.write",
"https://www.googleapis.com/auth/monitoring.write",
"https://www.googleapis.com/auth/service.management.readonly",
"https://www.googleapis.com/auth/servicecontrol",
"https://www.googleapis.com/auth/trace.append"
]
}
],
"startRestricted": false,
"status": "TERMINATED",
"tags": {
"fingerprint": "42WmSpB8rSM="
},
"zone": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a"
}
```

##### ACTUAL RESULTS

```json
ok: [localhost] => (item=my-test-instance) => {
"ansible_loop_var": "item",
"canIpForward": false,
"changed": false,
"cpuPlatform": "Unknown CPU Platform",
"creationTimestamp": "2020-04-21T06:19:23.517-07:00",
"deletionProtection": false,
"disks": [
{
"autoDelete": true,
"boot": true,
"deviceName": "my-test-instance",
"diskSizeGb": "10",
"guestOsFeatures": [
{
"type": "VIRTIO_SCSI_MULTIQUEUE"
}
],
"index": 0,
"interface": "SCSI",
"kind": "compute#attachedDisk",
"licenses": [
"https://www.googleapis.com/compute/v1/projects/debian-cloud/global/licenses/debian-9-stretch"
],
"mode": "READ_WRITE",
"source": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a/disks/my-test-instance",
"type": "PERSISTENT"
}
],
"displayDevice": {
"enableDisplay": false
},
"fingerprint": "wKws2l_yhiY=",
"id": "7680208216746314805",
"invocation": {
"module_args": {
"auth_kind": "serviceaccount",
"can_ip_forward": null,
"deletion_protection": false,
"disks": null,
"env_type": null,
"guest_accelerators": null,
"hostname": null,
"labels": null,
"machine_type": null,
"metadata": null,
"min_cpu_platform": null,
"name": "my-test-instance",
"network_interfaces": null,
"project": "my-test-project",
"scheduling": null,
"scopes": [
"https://www.googleapis.com/auth/compute"
],
"service_account_contents": null,
"service_account_email": null,
"service_account_file": "/Users//Downloads/my-test-project-c7549fc3f4db.json",
"service_accounts": [
{
"email": "71752527322-compute@developer.gserviceaccount.com",
"scopes": [
"https://www.googleapis.com/auth/devstorage.read_only",
"https://www.googleapis.com/auth/logging.write",
"https://www.googleapis.com/auth/monitoring.write",
"https://www.googleapis.com/auth/service.management.readonly",
"https://www.googleapis.com/auth/servicecontrol",
"https://www.googleapis.com/auth/trace.append"
]
}
],
"shielded_instance_config": null,
"state": "present",
"status": "TERMINATED",
"tags": null,
"zone": "us-central1-a"
}
},
"item": "my-test-instance",
"kind": "compute#instance",
"labelFingerprint": "42WmSpB8rSM=",
"machineType": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a/machineTypes/f1-micro",
"metadata": {
"ssh-keys": "omissis"
},
"name": "my-test-instance",
"networkInterfaces": [
{
"accessConfigs": [
{
"kind": "compute#accessConfig",
"name": "external-nat",
"networkTier": "PREMIUM",
"type": "ONE_TO_ONE_NAT"
}
],
"fingerprint": "fOIsyTl-u34=",
"kind": "compute#networkInterface",
"name": "nic0",
"network": "https://www.googleapis.com/compute/v1/projects/my-test-project/global/networks/default",
"networkIP": "10.128.0.9",
"subnetwork": "https://www.googleapis.com/compute/v1/projects/my-test-project/regions/us-central1/subnetworks/default"
}
],
"reservationAffinity": {
"consumeReservationType": "ANY_RESERVATION"
},
"scheduling": {
"automaticRestart": false,
"onHostMaintenance": "TERMINATE",
"preemptible": true
},
"selfLink": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a/instances/my-test-instance",
"startRestricted": false,
"status": "TERMINATED",
"tags": {
"fingerprint": "42WmSpB8rSM="
},
"zone": "https://www.googleapis.com/compute/v1/projects/my-test-project/zones/us-central1-a"
}
```

Please note that in the actual result I'm also expecting to see ( just under selflink ):
```json
"serviceAccounts": [
{
"email": "71752527322-compute@developer.gserviceaccount.com",
"scopes": [
"https://www.googleapis.com/auth/devstorage.read_only",
"https://www.googleapis.com/auth/logging.write",
"https://www.googleapis.com/auth/monitoring.write",
"https://www.googleapis.com/auth/service.management.readonly",
"https://www.googleapis.com/auth/servicecontrol",
"https://www.googleapis.com/auth/trace.append"
]
}
],
```
which is missing

Start by locating the gcp_compute_instance module entry point and reproduce the supplied playbook against an existing stopped VM. The issue names no files or tests; done means the requested service account and scopes are applied to the instance and the module reports the resulting state correctly.

Written by the indexing model from the issue text.