Proposal: Autoscaler shutdown instead of delete
Description
Currently Runner's docker+machine
executor removes the instances after idle time is reached. This effectively removes the instance and associated disk.
It can be useful to have an option to shutdown the instance instead of removing it. It will help to retain the cache across builds and will improve a lot build times. Many cloud providers like Google don't bill you for stopped instances, you only pay for storage, which is acceptable.
Proposal
Implement option to shutdown build instance instead of removing it. As an option we could specify different idle time, one for shutdown, and another one for removal.
This way for example we can say to shutdown the instance after it's idle for 1 hour, and remove it if it's idle for 7 days.