Fixed test_compare_volume_stats_values false failures

In case of several cinder_volumes, and multiple backends, we may get
results in unpredictable order, which makes test to fail.
Now we order list before comparison to get rid of such errors.
Another way is transforamtion to sets, but it will drop same tuples.

Example of the problem:
testtools.matchers._impl.MismatchError: !=:
reference = [(u'Open Source', u'ceph-hdd', u'ceph'),
    (u'Open Source', u'ceph-ssd', 'ceph'),
    (u'Open Source', u'ceph-ssd', 'ceph'),
    (u'Open Source', u'ceph-hdd', 'ceph')]
actual    = [(u'Open Source', u'ceph-hdd', u'ceph'),
    (u'Open Source', u'ceph-ssd', 'ceph'),
    (u'Open Source', u'ceph-hdd', 'ceph'),
    (u'Open Source', u'ceph-ssd', 'ceph')]

Change-Id: Ibd8a56368ec0091c106f31a3395c9dd313fda650
1 file changed