Plug alarm history logic into the API

The alarm scenario tests provide forward-looking coverage
which will be run as the storage backends' support for alarm
history lands.

A new config option alarm.record_history (defaulting to True)
guards the recording of alarm history.

Partially implements bp alarm-audit-api

Change-Id: I0c3bc348c86c7dc645cde3029a6fa76f9f767c37
Merge "Plug alarm history logic into the API"