check-rabbitmq-queue: Adjust threshholds for paging.

Ultimately, this isn't an effective way to monitor this queue; we want
time-based monitoring, not count-based monitoring.  Doing that
properly will likely involve modifying the queue processor to write
something about its status.

But until we add the monitoring we want, it makes sense to leave this
active with low limits.

scripts/nagios/check-rabbitmq-queue

@@ -14,14 +14,14 @@ WARN_THRESHOLD = {
     # The user_activity worker has high throughput and uses a
     # LoopQueueProcessingWorker, so it's normal to have a moderate
     # backlog.
-    'user_activity': 100,
+    'user_activity': 1000,
 }
 CRIT_THRESHOLD_DEFAULT = 50
 CRIT_THRESHOLD = {
     'missedmessage_emails': CRIT_THRESHOLD_DEFAULT,
     # A backlog of hundreds of events for user_activity likely
     # indicates an outage of the processor.
-    'user_activity': 500,
+    'user_activity': 5000,
 }
 
 states = {