The exception type is wrong and makes the except block not work

According to the context, it should be KeyError here to catch.
AttributeError will not happen here. More details could be found
in the bug report.

Change-Id: Id6351172703ac492e86475f75bf1be03f4e4e8a3
Closes-bug: #1506934
(cherry picked from commit 9d65841200)

neutron/agent/l3/ha.py

@@ -117,7 +117,7 @@ class AgentMixin(object):
 
         try:
             ri = self.router_info[router_id]
-        except AttributeError:
+        except KeyError:
             LOG.info(_LI('Router %s is not managed by this agent. It was '
                          'possibly deleted concurrently.'), router_id)
             return

neutron/tests/unit/agent/l3/test_agent.py

@@ -177,6 +177,13 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
             l3_agent.L3NATAgent(HOSTNAME, self.conf)
             self.ensure_dir.assert_called_once_with('/etc/ha/')
 
+    def test_enqueue_state_change_router_not_found(self):
+        agent = l3_agent.L3NATAgent(HOSTNAME, self.conf)
+        non_existent_router = 42
+
+        # Make sure the exceptional code path has coverage
+        agent.enqueue_state_change(non_existent_router, 'master')
+
     def test_periodic_sync_routers_task_raise_exception(self):
         agent = l3_agent.L3NATAgent(HOSTNAME, self.conf)
         self.plugin_api.get_routers.side_effect = ValueError