ofa_test_base: Fix NoSuchOptError in UT

Ensure setting up cfg.CONF.
Otherwise, depending on the execution order of tests,
some tests in test_ofa_neutron_agent can fail with
the following exception:

    NoSuchOptError: no such option: config_dir

The problem has been exposed by the recently merged change
for policy module, commit d83731a96d3b47fab1295de1fb53cfe30576619c .

Closes-Bug: #1392569
Change-Id: I0d38df0510b95160c67ea7b76ed413138fa3d770

neutron/tests/base.py

@@ -118,9 +118,9 @@ class BaseTestCase(sub_base.SubBaseTestCase):
         self.addCleanup(n_rpc.cleanup)
         n_rpc.init(CONF)
 
-    def setup_config(self):
+    def setup_config(self, args=None):
         """Tests that need a non-default config can override this method."""
-        self.config_parse()
+        self.config_parse(args=args)
 
     def config(self, **kw):
         """Override some configuration values.

neutron/tests/unit/ofagent/ofa_test_base.py

@@ -69,3 +69,4 @@ class OFAAgentTestBase(OFATestBase):
                        help='openflow tcp listen port')
         ])
         cfg.CONF.set_override('root_helper', 'fake_helper', group='AGENT')
+        super(OFATestBase, self).setup_config()

neutron/tests/unit/test_db_plugin.py

@@ -155,7 +155,7 @@ class NeutronDbPluginV2TestCase(testlib_api.WebTestCase,
         # If test_config specifies some config-file, use it, as well
         for config_file in test_lib.test_config.get('config_files', []):
             args.extend(['--config-file', config_file])
-        self.config_parse(args=args)
+        super(NeutronDbPluginV2TestCase, self).setup_config(args=args)
 
     def _req(self, method, resource, data=None, fmt=None, id=None, params=None,
              action=None, subresource=None, sub_id=None, context=None):