random test failure: unable to attach volume: invalid empty address of replica

[yasker]

 ApiError: (ApiError(...), 'Server Error : unable to attach volume: failed to start the controller for volume \'longhorn-manager-test_vol-1.0\': Fail to create controller for longhorn-manager-test_vol-1.0: invalid empty address of replica longhorn-manager-test_vol-1.0-replica-c337e1e6-eeab-4a12\n{\'self\': <function <lambda> at 0x7f2814c86c08>, \'message\': u"unable to attach volume: failed to start the controller for volume \'longhorn-manager-test_vol-1.0\': Fail to create controller for longhorn-manager-test_vol-1.0: invalid empty address of replica longhorn-manager-test_vol-1.0-replica-c337e1e6-eeab-4a12", \'detail\': u\'\', \'type\': u\'error\', \'code\': u\'Server Error\', \'actions\': {}, \'links\': {\'self\': u\'http://172.17.0.5:9500/v1/volumes/longhorn-manager-test_vol-1.0\'}, \'status\': 500}')

[yasker]

It's a race condition in writing the Volume object. Working on a fix.