Possible vm states for instances.
Compute instance vm states represent the state of an instance as it pertains to a user or administrator.
vm_state describes a VM’s current stable (not transition) state. That is, if there is no ongoing compute API calls (running tasks), vm_state should reflect what the customer expect the VM to be. When combined with task states (task_states.py), a better picture can be formed regarding the instance’s health and progress.