Use more specific asserts in tests

Instead of assertTrue and assertFalse use more specific asserts.
They are compatible with Python 2.7[1] and 3.4[2]

[1]: https://docs.python.org/2.7/library/unittest.html
[2]: https://docs.python.org/3.4/library/unittest.html

Change-Id: I3ac49863641e26841210d020e8bca0bd93176423
diff --git a/tempest/api/volume/admin/test_multi_backend.py b/tempest/api/volume/admin/test_multi_backend.py
index 120dbb1..5703313 100644
--- a/tempest/api/volume/admin/test_multi_backend.py
+++ b/tempest/api/volume/admin/test_multi_backend.py
@@ -129,7 +129,7 @@
         volume1_host = volume['os-vol-host-attr:host']
         msg = ("multi-backend reporting incorrect values for volume %s" %
                volume_id)
-        self.assertTrue(len(volume1_host.split("@")) > 1, msg)
+        self.assertGreater(len(volume1_host.split("@")), 1, msg)
 
     def _test_backend_name_distinction(self, volume_id_list):
         # this test checks that the volumes created at setUp don't