DVR Floating IP create don't raise exception if agent not found

Patch [1] added handling of AgentNotFoundByTypeHost exception in
create_fip_agent_gw_port_if_not_exists method in
neutron.db.l3_dvr_db.DVRResourceOperationHandler class.
Unfortunatelly there was mistake there and such exception wasn't
catched properly.
That caused issue e.g. in functional-python35 tests but wasn't catched
properly in functional tests using python27.

This patch changes this to handle such exception properly.

[1] https://review.openstack.org/#/c/574917/

Change-Id: If43f2c944ff46d8b05fbcf68231fd04bed147ba0

neutron/db/l3_dvr_db.py

@@ -983,8 +983,7 @@ class _DVRAgentInterfaceMixin(object):
         try:
             l3_agent_db = self._get_agent_by_type_and_host(
                 context, const.AGENT_TYPE_L3, host)
-        except agent_exc.AgentNotFoundByTypeHost(
-            agent_type=const.AGENT_TYPE_L3, host=host):
+        except agent_exc.AgentNotFoundByTypeHost:
             LOG.warning("%(ag)s agent not found for the given host: %(host)s",
                         {'ag': const.AGENT_TYPE_L3,
                          'host': host})

neutron/tests/functional/services/l3_router/test_l3_dvr_router_plugin.py

@@ -20,7 +20,6 @@ from neutron_lib.api.definitions import portbindings
 from neutron_lib.callbacks import events
 from neutron_lib.callbacks import registry
 from neutron_lib.callbacks import resources
-from neutron_lib.exceptions import agent as agent_exc
 
 from neutron_lib import constants
 from neutron_lib import context
@@ -338,12 +337,9 @@ class L3DvrTestCase(L3DvrTestCaseBase):
                 self.context, router['id'],
                 {'subnet_id': int_subnet['subnet']['id']})
             if test_agent_mode is None:
-                self.assertRaises(
-                    agent_exc.AgentNotFoundByTypeHost,
-                    self.l3_plugin.create_fip_agent_gw_port_if_not_exists,
-                    self.context,
-                    ext_net_id,
-                    'host1')
+                self.assertIsNone(
+                    self.l3_plugin.create_fip_agent_gw_port_if_not_exists(
+                        self.context, ext_net_id, 'host1'))
                 return
             floating_ip = {'floating_network_id': ext_net_id,
                            'router_id': router['id'],