Error migrating vault backend from raft to s3

**Describe the bug**
Recentñy we want to change standalone vault to HA mode. To do it, we do the migration with the command of migrate, and the config (migrate-old.hcl):
```
storage_source "s3" {
bucket = "namebucket"
region = "region"
access_key = "AWS access key"
secret_key = "AWS secret key"
}

storage_destination "raft" {
path = "/vault/data"
node_id = "vault-0"
}
cluster_addr = "http://vault-0.vault-internal:8201"
```
We try to migrate the new vault backend from Raft to s3 again. When try to do it, we put the HA mode in standby into node, and try to run the migration config (migrate.hcl):
```
storage_source "raft" {
path = "/vault/data/raft"
}

storage_source "s3" {
bucket = "namebucket-new"
region = "region"
access_key = "AWS access key"
secret_key = "AWS secret key"
}

```
And the success message showed, but no info is backed into s3 bucket (if no exist, show error that backend s3 unrechable).

**To Reproduce**
Steps to reproduce the behavior:
1. Install chart
2. Run vault command
```
$ vault operator migrate -config /home/vault/migrate.hcl
Success! All of the keys have been migrated.
```
3. See error (vault logs, etc.) --> No logs show into vault pod of migration running

**Expected behavior**
The Raft info should be copied into new s3 bucket.

**Environment**
* Kubernetes version: 1.17
* Distribution or cloud vendor (OpenShift, EKS, GKE, AKS, etc.): EKS
* Other configuration options or runtime services (istio, etc.):
* vault-helm version: 0.12.0

Chart values:

```yaml
global:
tlsDisable: false
injector:
enabled: false
server:
image:
tag: "1.7.2"
dataStorage:
size: 2Gi
storageClass: "class-sc"
extraSecretEnvironmentVars:
- envName: AWS_ACCESS_KEY_ID
secretName: vault-conf
secretKey: aws-secret-access-key
- envName: AWS_SECRET_ACCESS_KEY
secretName: vault-conf
secretKey: aws-secret-key
- envName: VAULT_AWSKMS_SEAL_KEY_ID
secretName: vault-conf
secretKey: kms-key-id
extraEnvironmentVars:
VAULT_CACERT: /vault/tls/ca.crt
volumes:
- name: tls
secret:
secretName: vault-tls
volumeMounts:
- mountPath: /vault/tls
name: tls
readOnly: true
ha:
enabled: true
replicas: 3
raft:
enabled: true
setNodeId: true
config: |
ui = true

listener "tcp" {
tls_disable = "false"
address = "[::]:8200"
cluster_address = "[::]:8201"
tls_cert_file = "/vault/tls/tls.crt"
tls_key_file = "/vault/tls/tls.key"
tls_client_ca_file = "/vault/tls/ca.crt"
}

storage "raft" {
path = "/vault/data"

retry_join {
leader_api_addr = "https://vault-0.vault-internal:8200"
leader_client_cert_file = "/vault/tls/tls.crt"
leader_client_key_file = "/vault/tls/tls.key"
leader_ca_cert_file = "/vault/tls/ca.crt"
}
retry_join {
leader_api_addr = "https://vault-1.vault-internal:8200"
leader_client_cert_file = "/vault/tls/tls.crt"
leader_client_key_file = "/vault/tls/tls.key"
leader_ca_cert_file = "/vault/tls/ca.crt"
}
retry_join {
leader_api_addr = "https://vault-2.vault-internal:8200"
leader_client_cert_file = "/vault/tls/tls.crt"
leader_client_key_file = "/vault/tls/tls.key"
leader_ca_cert_file = "/vault/tls/ca.crt"
}

}
seal "awskms" {
region = "region"
}

disable_mlock = true
cluster_addr = "https://vault-0.vault-internal:8201"

service_registration "kubernetes" {}
ui:
enabled: true
publishNotReadyAddresses: true
activeVaultPodOnly: false
serviceType: "ClusterIP"
serviceNodePort: null
externalPort: 80
```

**Additional context**
Add any other context about the problem here.