Emit start and end versioned notifications at the start and at the end of the given action

The bug https://bugs.launchpad.net/nova/+bug/1763051 showed that the start and end notifications are not always placed at the start and the end of the respective code path.
The aim of this bp is:
* to define the rules where the start and end notifications should be placed in the code path. E.g. most of the instance action start notifications are emitted from the compute/manager not from the REST API where the action is initiated. But in the other hand instance.delete in case of local delete is emitted from compute/api
* think about using decorator and / or a context manager to send notifications at function enter/exit/error
* to go through the versioned notifications and make them consistently placed