testtools.matchers._impl.MismatchError: 'completed' != u'running' in test_bug_1718512.TestRequestSpecRetryReschedule.test_resize_with_reschedule_then_live_migrate

[Environment]
nova master(commit 15f1caf98a46ba0ab3f8365075c564e89f06eef3)
Ubuntu 16.04.2 LTS

[Step to reproduce]
tox -e functional nova.tests.functional.regressions.test_bug_1718512.TestRequestSpecRetryReschedule.test_resize_with_reschedule_then_live_migrate

[Log]

nova.tests.functional.regressions.test_bug_1718512.TestRequestSpecRetryReschedule.test_resize_with_reschedule_then_live_migrate
-------------------------------------------------------------------------------------------------------------------------------

Captured stderr:
~~~~~~~~~~~~~~~~
    /tmp/nova/.tox/functional/local/lib/python2.7/site-packages/paste/deploy/loadwsgi.py:22: DeprecationWarning: Parameters to load are deprecated. Call .resolve and .require separately.
      return pkg_resources.EntryPoint.parse("x=" + s).load(False)

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):
      File "nova/tests/functional/regressions/test_bug_1718512.py", line 150, in test_resize_with_reschedule_then_live_migrate
        self.assertEqual('completed', migrations[0]['status'])
      File "/tmp/nova/.tox/functional/local/lib/python2.7/site-packages/testtools/testcase.py", line 411, in assertEqual
        self.assertThat(observed, matcher, message)
      File "/tmp/nova/.tox/functional/local/lib/python2.7/site-packages/testtools/testcase.py", line 498, in assertThat
        raise mismatch_error
    testtools.matchers._impl.MismatchError: 'completed' != u'running'

See an attached file in comment #1 for more detail.

It also occurs in the gate check job (nova-tox-functional).

http://logs.openstack.org/67/560267/1/check/nova-tox-functional/550e5a1/job-output.txt.gz