Correctly set CombinationAlarm repeat_actions

Previously, the value of the repeat_actions property has no effect on
combination alarm creation, so this attribute defaulted to false on the
Ceilometer side, breaking Heat autoscaling.

Now, this attribute is set correctly as a top-level attribute on the
alarm.

Closes-Bug: #1394159

Change-Id: I1335d5664e9f3f408fbe6815d6cd6fd0a75ba1b8
(cherry picked from commit 02ec693a4701f3423be811a3a5de334c78744465)
Merge "Correctly set CombinationAlarm repeat_actions" into stable/juno