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: I2dae60fe786a99344fc12dd4aeaea9c79c9811c5
diff --git a/manila_tempest_tests/tests/api/admin/test_multi_backend.py b/manila_tempest_tests/tests/api/admin/test_multi_backend.py
index 8aeabc3..79c9c19 100644
--- a/manila_tempest_tests/tests/api/admin/test_multi_backend.py
+++ b/manila_tempest_tests/tests/api/admin/test_multi_backend.py
@@ -61,7 +61,7 @@
         # Share's 'host' should be like "hostname@backend_name"
         for share in self.shares:
             get = self.shares_client.get_share(share['id'])
-            self.assertTrue(len(get["host"].split("@")) == 2)
+            self.assertEqual(2, len(get["host"].split("@")))
 
     @tc.attr(base.TAG_POSITIVE, base.TAG_API_WITH_BACKEND)
     def test_share_share_type(self):