Support post action to composed node for Valence

Valence should provide separate api entry to allow user to post action to composed node, like Power On/Off, Force Shutdown/Restart, etc. And another api entry to get all allowable actions for the composed node.

RSC controller for Valence

A controller service for life-cycle management of rack-scale hardware resources. This service (a) keeps track of discovered components, composed, booted, shutdown and released nodes. (b) exposes the capabilities of the rack to OpenStack.