Added reservation policy support.
With reservation policy user can use the reserved resources
by blazar to create VNF.
Implements: blueprint reservation-vnfm
This patch adds below functionality:
- New policy action ``vdu_autoheal`` for recovering failed VDUs
as reported by the respective monitoring driver configured in
the monitoring policy of the VNFD template.
- Add unit/functional tests.
- Added oslo_versioned library to implement HealVnfRequest object.
Note: The implementation of vdu_autoheal policy action will support
HealVnfRequest interface as mentioned in the ETSI standard 
Implements: blueprint vdu-auto-healing
Currently, backend actions are tightly coupled with monitor module.
This is like a barrier when we have a various actions in the future.
Also, it will be good for separating monitoring-related features out
from tacker-server. This patch also proposes a policy action framework so
that VNF operators can easily add their own actions.
This patch will focus on:
1. Fixing hardcoded metadata
2. Adding functional test for alarm monitor
3. Refactoring tosca template for alarm monitor
4. Refactoring scaling in/out support in alarm monitor
5. Supporting multi-trigger
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