Use more specific asserts

Many places, there are more specific asserts which can be used.
I replaced the generic assert with more specific ones, where
it was possible.

This change enhances readibility, and on fail, more useful
message is displayed

Change-Id: I86a6baeae2cd36610a2be10ae5085555246c368a

watcher/tests/decision_engine/test_sync.py

@@ -376,7 +376,8 @@ class TestSyncer(base.DbTestCase):
 
         self.assertEqual(2, strategy2.goal_id)
         self.assertIn(strategy2.name, created_strategies)
-        self.assertTrue(strategy2.id != created_strategies[strategy2.name].id)
+        self.assertNotEqual(strategy2.id,
+                            created_strategies[strategy2.name].id)
 
         self.assertEqual(set([audit_template2.id,
                               audit_template3.id,