an unreleased version of cinder fails a test when run with python 2.7 from the branch.  I don't have a test case yet, but looking at the error message and list of fixed issues after the 2.7.9 release, the fix for issue #23098 could be the culprit.

FAIL: cinder.tests.test_utils.GetBlkdevMajorMinorTestCase.test_get_blkdev_major_minor_file
cinder.tests.test_utils.GetBlkdevMajorMinorTestCase.test_get_blkdev_major_minor_file
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_StringException: Traceback (most recent call last):
  File "/build/buildd/cinder-2015.1~b3/cinder/tests/test_utils.py", line 721, in test_get_blkdev_major_minor_file
    dev = self._test_get_blkdev_major_minor_file('/dev/made_up_disk1')
  File "/usr/lib/python2.7/dist-packages/mock.py", line 1210, in patched
    return func(*args, **keywargs)
  File "/build/buildd/cinder-2015.1~b3/cinder/tests/test_utils.py", line 712, in _test_get_blkdev_major_minor_file
    dev = utils.get_blkdev_major_minor(test_file)
  File "/build/buildd/cinder-2015.1~b3/cinder/utils.py", line 656, in get_blkdev_major_minor
    return get_blkdev_major_minor(devpath, False)
  File "/build/buildd/cinder-2015.1~b3/cinder/utils.py", line 645, in get_blkdev_major_minor
    return '%d:%d' % (os.major(st.st_rdev), os.minor(st.st_rdev))
SystemError: ../Objects/longobject.c:998: bad argument to internal function
Traceback (most recent call last):
_StringException: Empty attachments:
  stderr
  stdout