GCP: Add option to configure minimum number of instances

[Mohsen Rezaei (mohsenrezaeithe)]

Fixes #30

On the UI

1. Configurable in the image configs:
   
2. Visible on the profile page:
   

On the server
The quota check guards the minimum number of instances that must be kept alive at all times for the image group:

[2019-09-17 07:02:54,749]   INFO [uled executor 3] - te.IdleTimeoutTerminateFactory - Will stop instance GoogleCloudInstance{myName='poc-tcagent-poc-stg2-1567103841-1040'}, profile 'GCP POC staging'{id=google-1, projectId=_Root} with idle time 12 minutes (idle time is 3 minutes)
[2019-09-17 07:02:54,749]   INFO [uled executor 3] - l.instances.StopInstanceAction - Terminating instance 'poc-tcagent-poc-stg2-1567103841-1040', profile 'GCP POC staging'{id=google-1, projectId=_Root}, reason: "Idle timeout reached"
[2019-09-17 07:02:54,749]   INFO [uled executor 3] - r.impl.DBCloudStateManagerImpl - Image: GoogleCloudImage{myName='poc-tcagent-poc-stg2-1567103841-'}, profile: profile 'GCP POC staging'{id=google-1, projectId=_Root} was marked to CONTAIN agent
[2019-09-17 07:02:54,758]   INFO [uled executor 3] - clouds.google.GoogleCloudImage - Unable to terminate anymore instances. Configured minimum limit has reached (min: 1)

[Mohsen Rezaei (mohsenrezaeithe)]

Did some more testing, and it looks like the return on terminateInstance() causes something to mark the agent as CONTAIN:

[2019-09-17 06:57:54,656]   INFO [uled executor 2] - r.impl.DBCloudStateManagerImpl - Image: GoogleCloudImage{myName='poc-tcagent-poc-stg2-1567103841-'}, profile: profile 'GCP POC staging'{id=google-1, projectId=_Root} was marked to CONTAIN agent

which I'm assuming is also related to this warning on the profile:

Any suggestion on what's the best way to achieve the minimum number limitation?

[Mohsen Rezaei (mohsenrezaeithe)]

@dimyriy Dmitry Treskunov (@dmitry-treskunov) is this something that can be pulled into the profiles implementation, or needs to be implemented on the server?