Phase represents the different stages blue-green upgrade is
running in.
Values:
PHASE_UNSPECIFIED (0):
Unspecified phase.
UPDATE_STARTED (1):
blue-green upgrade has been initiated.
CREATING_GREEN_POOL (2):
Start creating green pool nodes.
CORDONING_BLUE_POOL (3):
Start cordoning blue pool nodes.
WAITING_TO_DRAIN_BLUE_POOL (8):
Start waiting after cordoning the blue pool
and before draining it.
DRAINING_BLUE_POOL (4):
Start draining blue pool nodes.
NODE_POOL_SOAKING (5):
Start soaking time after draining entire blue
pool.
DELETING_BLUE_POOL (6):
Start deleting blue nodes.
ROLLBACK_STARTED (7):
Rollback has been initiated.