Merge extension server-start-stop into servers core API v3

* Move the action 'start' and 'stop' into servers core and
the corresponding unittest.
* Add decorator extensions.expected_errors

Partially implements bp v3-api-extension-versioning

Change-Id: I94acb688e0a7975b67d652d11d315843dbdf3eb3
Merge "Merge extension server-start-stop into servers core API v3"