Fix test_live_configuration

This test, which is currently passing, lacked a pause which could
cause it to erroneously pass even when broken.  Update the test
to include it.

Change-Id: Ic4391d4a80489daaffdcff2f2012f3a252dbc0db

tests/unit/test_scheduler.py

@@ -2395,6 +2395,7 @@ class TestScheduler(ZuulTestCase):
         self.waitUntilSettled()
 
         self.sched.reconfigure(self.config)
+        self.waitUntilSettled()
 
         self.launch_server.hold_jobs_in_build = False
         self.launch_server.release()