heat API : Implement initial CloudWatch API

heat API : Implement initial CloudWatch API

Initial AWS-compatible CloudWatch API implementation
Supports the following API actions:
- DescribeAlarms : describe alarm/watch details
- ListMetrics : List watch metric datapoints
- PutMetricData : Create metric datapoint
- SetAlarmState : temporarily set alarm state

Skeleton implementation of all other TODO actions which
returns HeatAPINotImplementedError.

Only basic filtering parameters supported at this time.

Signed-off-by: Steven Hardy <shardy@redhat.com>
Change-Id: I8628854a135fff07b675e85150ea0b50184ed2e1