Add basic InstanceAction object

This adds a basic InstanceAction object with the ability to provide
the functionality needed to satisfy compute_api's use of actions.
The ability to finish an action by uuid in a sort of out-of-body
way (as it is done now) is provided, as well as an instance method
for a (hopefully) future scenario where actions are started, carried,
and finished when appropriate.

Related to blueprint compute-api-objects

Change-Id: I094645b065575bbbce35ed18bf6901cbbf4e383d
Merge "Add basic InstanceAction object"