Don't evaluate ceilometer watchrules

If you have both Ceilometer and cwlite alarms in one stack (a little odd)
we try to evaluate Ceilometer alarms in the periodic task.

Change-Id: Ia75bf1e5cfa3e2ac31242eafd5fa96d757786ada
Closes-bug: #1375111
Merge "Don't evaluate ceilometer watchrules"