Revert "service: replace eventlet event by threading"

This reverts commit f08f6ba7e80729fb6028b24568da0f651a75fcd6.

This was a terrible idea: as soon as you don't monkey patch threading,
this does not work as expected in the end.

So it's better to say that it's explicitly eventlet mechanisms that are
required, at least for now.

Conflicts:
	tests/unit/test_service.py

Partial-Bug: #1274044

Change-Id: I4d4f112d4550d912c4f81e62bc9a4714cf117384
Move the released file lock to the successful path

Instead of logging that the lock was released even
if there was an error that caused it not to be
unreleased we should only log that it was released
after it really was.

Change-Id: Id3f37b801a1d5efd2dcb4a9803989df50a36e7de
Merge "Revert "service: replace eventlet event by threading""
Merge "Move the released file lock to the successful path"