Values:
STATE_UNSPECIFIED (0):
The storage volume is in an unknown state.
CREATING (1):
The storage volume is being created.
READY (2):
The storage volume is ready for use.
DELETING (3):
The storage volume has been requested to be
deleted.
UPDATING (4):
The storage volume is being updated.
COOL_OFF (5):
The storage volume is in cool off state. It will be deleted
after expire_time.