New alarm evaluator for handling alarms on events

New alarm evaluator for handling alarms on events

NOTE: This is blueprint spec draft for OpenStack Ceilomter.

This blueprint proposes to add a new alarm evaluator for handling
alarms on events passed from other OpenStack services, that provides
event-driven alarm evaluation which makes new sequence in Ceilometer
instead of the polling-based approach of the existing Alarm Evaluator,
and realizes immediate alarm notification to end users.

JIRA: DOCTOR-3
Change-Id: Ie1a50111d82ad3c808c8ec2350e15119165cebff
Signed-off-by: Ryota MIBU <r-mibu@cq.jp.nec.com>