Nomad lifecyle prestart/non-sidecar task not restarting(before main task) when reboot node

### Nomad version
Nomad v0.12.0 (8f7fbc8e7b5a4ed0d0209968faf41b238e6d5817)

### Operating system and Environment details
Centos 7.5 VM env on virtualbox 6.1

### Issue
For a `main` task which depends on the output of the `prestart` task, for example, a output file at shared `alloc` dir, in this case. When restarting the nomad host, and the output file in the `alloc` dir has been `garbage collected`(A guess, not 100% sure), while the `pretask` is not executed, which lead to the main task always fail.

From the alloc status of the prestart task, it only shows the task received log :

```
2021-01-18T12:06:51Z Received Task received by client
```

From the understanding of `main`/`prestart` task's dependency, like the example of waiting for db ready at https://www.nomadproject.io/docs/job-specification/lifecycle
It looks `prestart` task can't be a one-time only job. Restarting the `main` task should always restart the `prestart` task.

Also the reboot test below shows the issue that, there is no reliable way to pass the output from one task to another dependent task, by using the shared alloc dir.

### Reproduction steps
- Update nomad.hcl with the config ` client { gc_max_allocs = 1 }`, for quickly reproduce the issue
- Run the following job file with nomad job run
- Show the job status
```
nomad job status test
ID = test
Name = test
Submit Date = 2021-01-18T11:47:41Z
Type = service
Priority = 50
Datacenters = dc1
Namespace = default
Status = running
Periodic = false
Parameterized = false

Summary
Task Group Queued Starting Running Failed Complete Lost
test 0 0 1 0 0 0

Latest Deployment
ID = ff4a14b1
Status = running
Description = Deployment is running

Deployed
Task Group Desired Placed Healthy Unhealthy Progress Deadline
test 1 1 0 0 2021-01-18T11:57:41Z

Allocations
ID Node ID Task Group Version Desired Status Created Modified
df20b14a 1d358dc0 test 0 run running 15s ago 7s ago

```

```
nomad alloc status df20b14a
ID = df20b14a-9242-1925-bb4f-ba955df54a82
Eval ID = 8bb6ff37
Name = test.test[0]
Node ID = 1d358dc0
Node Name = bne_dev4
Job ID = test
Job Version = 0
Client Status = running
Client Description = Tasks are running
Desired Status = run
Desired Description =
Created = 23s ago
Modified = 5s ago
Deployment ID = ff4a14b1
Deployment Health = healthy

Task "test-pre" (prestart) is "dead"
Task Resources
CPU Memory Disk Addresses
0/100 MHz 0 B/300 MiB 300 MiB

Task Events:
Started At = 2021-01-18T11:47:42Z
Finished At = 2021-01-18T11:47:42Z
Total Restarts = 0
Last Restart = N/A

Recent Events:
Time Type Description
2021-01-18T11:47:42Z Terminated Exit Code: 0
2021-01-18T11:47:42Z Started Task started by client
2021-01-18T11:47:41Z Task Setup Building Task Directory
2021-01-18T11:47:41Z Received Task received by client

Task "test" is "running"
Task Resources
CPU Memory Disk Addresses
0/100 MHz 156 KiB/300 MiB 300 MiB

Task Events:
Started At = 2021-01-18T11:47:49Z
Finished At = N/A
Total Restarts = 0
Last Restart = N/A

Recent Events:
Time Type Description
2021-01-18T11:47:49Z Started Task started by client
2021-01-18T11:47:42Z Driver Downloading image
2021-01-18T11:47:42Z Task Setup Building Task Directory
2021-01-18T11:47:41Z Received Task received by client
```
- Reboot(repeat reboot) the node, until the job is at `pending` state
- Show the job status
```
nomad job status test
ID = test
Name = test
Submit Date = 2021-01-18T11:47:41Z
Type = service
Priority = 50
Datacenters = dc1
Namespace = default
Status = running
Periodic = false
Parameterized = false

Summary
Task Group Queued Starting Running Failed Complete Lost
test 0 1 0 0 1 0

Latest Deployment
ID = ff4a14b1
Status = successful
Description = Deployment completed successfully

Deployed
Task Group Desired Placed Healthy Unhealthy Progress Deadline
test 1 1 1 0 2021-01-18T11:57:59Z

Allocations
ID Node ID Task Group Version Desired Status Created Modified
df20b14a 1d358dc0 test 0 run pending 20m12s ago 8s ago
```

```
nomad alloc status df20b14a
ID = df20b14a-9242-1925-bb4f-ba955df54a82
Eval ID = 8bb6ff37
Name = test.test[0]
Node ID = 1d358dc0
Node Name = bne_dev4
Job ID = test
Job Version = 0
Client Status = pending
Client Description = No tasks have started
Desired Status = run
Desired Description =
Created = 20m19s ago
Modified = 2s ago
Deployment ID = ff4a14b1
Deployment Health = healthy

Task "test-pre" (prestart) is "dead"
Task Resources
CPU Memory Disk Addresses
100 MHz 300 MiB 300 MiB

Task Events:
Started At = 2021-01-18T11:47:42Z
Finished At = 2021-01-18T11:47:42Z
Total Restarts = 0
Last Restart = N/A

Recent Events:
Time Type Description
**2021-01-18T12:06:51Z Received Task received by client**
2021-01-18T11:47:42Z Terminated Exit Code: 0
2021-01-18T11:47:42Z Started Task started by client
2021-01-18T11:47:41Z Task Setup Building Task Directory
2021-01-18T11:47:41Z Received Task received by client

Task "test" is "pending"
Task Resources
CPU Memory Disk Addresses
0/100 MHz 164 KiB/300 MiB 300 MiB

Task Events:
Started At = 2021-01-18T12:07:41Z
Finished At = N/A
Total Restarts = 4
Last Restart = 2021-01-18T12:07:46Z

Recent Events:
Time Type Description
2021-01-18T12:07:58Z Driver Downloading image
2021-01-18T12:07:46Z Restarting Task restarting in 12.425820555s
2021-01-18T12:07:46Z Terminated Exit Code: 1, Exit Message: "Docker container exited with non-zero exit code: 1"
2021-01-18T12:07:41Z Started Task started by client
2021-01-18T12:07:33Z Driver Downloading image
2021-01-18T12:07:21Z Restarting Task restarting in 11.619813438s
2021-01-18T12:07:21Z Terminated Exit Code: 1, Exit Message: "Docker container exited with non-zero exit code: 1"
2021-01-18T12:07:16Z Started Task started by client
2021-01-18T12:07:08Z Driver Downloading image
2021-01-18T12:06:57Z Restarting Task restarting in 11.438944209s

```

### Job file (if appropriate)

```hcl
job "test" {
datacenters = ["dc1"]
type = "service"

group "test" {
restart {
interval = "6m"
attempts = 10
delay = "10s"
mode = "delay"
}

# add prestart task
task "test-pre" {
driver = "docker"
lifecycle {
hook = "prestart"
sidecar = false
}

config {
image = "alpine:3.8"
command = "sh"

args = ["-c", "echo test > /alloc/test_file"]
}
}

task "test" {
driver = "docker"

config {
image = "alpine:3.8"
command = "sh"

args = ["-c", "if [ ! -s /alloc/test_file ]; then sleep 5; exit 1; else while sleep 3600; do :; done; fi"]
}
}
}
}
```