* Implement restart policy for VMs
* Do not update VM.Resource, we only use it as a read-only specification
* Err()/setErr(): use atomic.Pointer instead of sync.Mutex
* Fail VMs if the worker had crashed/is unhealthy
* OnDiskName: properly handle cases when VM's name contains hyphens
* Worker: introduce Offline() method and check it before scheduling
* tart.List(): use Tart's JSON output
* OnDiskName: remove empty parts check
* Scheduler: move health-checking logic to a separate function
* Only fail "running" VMs
* Only fail orphaned VMs if they're in terminal state
* Integration tests
* Run healthCheckingLoopIteration() before schedulingLoopIteration()
* Worker: sync on-disk VMs only once at start
Nikolay Edigaryev