Test: make enforce_type=True in CONF.set_override and fix error

Each config option has limitation for type and value.
We make enforce_type=True to check whether we pass wrong type.

Also fixes a type error issue in test_db_manager.py.

Change-Id: I6e111e21588525d32b05eeba75b06583d4e605ed
Related-Bug: #1517839

watcher/tests/db/base.py

@@ -90,7 +90,8 @@ class Database(fixtures.Fixture):
 class DbTestCase(base.TestCase):
 
     def setUp(self):
-        cfg.CONF.set_override("enable_authentication", False)
+        cfg.CONF.set_override("enable_authentication", False,
+                              enforce_type=True)
         super(DbTestCase, self).setUp()
 
         self.dbapi = dbapi.get_instance()