Hopefully solved my angle issues
Fixed issues when introspection server not running
Removed useless member in introspection server
Make sure each task is in a separate thread

This does not play well with the ThreadPool concept of futures: it
tries to reuse the same threads. Need to find a better way to
identify tasks (like future ID).
Behave better when introspection name server is not started
Added introspection support for the 'waiting' state
[minor] improve logging msg
Reworked the tracking of action ID

Uses a custom version of concurrent.ThreadPoolExecutor and concurrent.Future.

This should allow to accurately track the progress of the
different actions.
Added a 'ping' mechanism in the introspection server that act as a watchdog