Add missing explicit cfg option import

The test ceilometer.tests.event.test_endpoint.TestEventEndpoint cannot
be run standalone because of missing import.

This change fixes that.

Change-Id: I18083a0793204da5ef9b78573fa4a0483964e158

ceilometer/tests/event/test_endpoint.py

@@ -19,6 +19,7 @@
 
 import mock
 
+from oslo.config import cfg
 import oslo.messaging
 from stevedore import extension
 
@@ -80,6 +81,10 @@ TEST_NOTICE_PAYLOAD = {
 }
 
 
+cfg.CONF.import_opt('store_events', 'ceilometer.notification',
+                    group='notification')
+
+
 class TestEventEndpoint(tests_base.BaseTestCase):
 
     def setUp(self):