Automatic triggering Action Plans

Description:
This blueprint goes beyond the "continuously-optimization" blueprint [1] by applying automatically the Action Plans.

Problem:
Watcher needs to continuously optimize the OpenStack cloud for a specific strategies or goals. Watcher can periodically trigger some Audits which generates Action Plans.
Unfortunately, in the current implementation the Administrator have to launch manually
the recommended Action Plan in order to apply it on the real system.

Proposal:
We should add the feature "automatic triggering". If the Audit has an 'automatic triggering' of the Action Plan, the Watcher module will automatically launch it at the most appropriate time.

Note: that some Action Plan may consist in executing some actions at a given date & time. so, we should pay attention of execution order of the Action Plans.
We should aslo add a deadline for executing the audit and applying the audits. (maybe out of scope of this blueprint)

[1] https://blueprints.launchpad.net/watcher/+spec/continuously-optimization