Allow tests from test_dhcp_agent run independently

Some tests from test_dhcp_agent depend on each other
and cannot be run in arbitrary order. TestDhcpAgent
and TestDhcpAgentEventHandler need config options that
are initialized in other tests. This patch eliminates
such dependencies.

Fixes: bug #1125951
Change-Id: I10bc46a5e1244ea0f7a05a20bb162c50303f282e

quantum/tests/unit/test_dhcp_agent.py

@@ -86,6 +86,7 @@ def __str__(self):
 
 class TestDhcpAgent(unittest.TestCase):
     def setUp(self):
+        cfg.CONF.register_opts(dhcp_agent.DeviceManager.OPTS)
         cfg.CONF.register_opts(dhcp_agent.DhcpAgent.OPTS)
         cfg.CONF.register_opts(dhcp_agent.DhcpLeaseRelay.OPTS)
         self.driver_cls_p = mock.patch(
@@ -267,6 +268,7 @@ def test_periodoc_resync_helper(self):
 class TestDhcpAgentEventHandler(unittest.TestCase):
     def setUp(self):
         cfg.CONF.register_opts(dhcp_agent.DeviceManager.OPTS)
+        cfg.CONF.register_opts(dhcp_agent.DhcpLeaseRelay.OPTS)
         cfg.CONF.set_override('interface_driver',
                               'quantum.agent.linux.interface.NullDriver')
         config.register_root_helper(cfg.CONF)