To support both CW and CM, return alarmurl from policy ref

This is so we can still have the following:
  AlarmActions:
  - {Ref: ServerScaleUpPolicy}

and use Ceilometer underneath.

The watchrule now tries to look up the resource by
both name and resource_by_refid.

Change-Id: I4759806919ab4f3ccef66698235b23f7f310cb03
Add a CloudWatch::Alarm implementation based on Ceilometer

It's off by default for the moment so the current cloudwatch tests can run.

Change-Id: Ibdce9c9223969bdcb8f2368e98dc6ab1241b84df
Use string constants to prevent typo errors

Change-Id: If8fccaa3f5d77698a50f803c2b97b85c5a7613ea
Merge "To support both CW and CM, return alarmurl from policy ref"
Merge "Add a CloudWatch::Alarm implementation based on Ceilometer"
Merge "Use string constants to prevent typo errors"