Fix IDEX-1379 Ability to stop run earlier

With a new method RunQueue#stop called from RunnerService#stop the run
can now be put in a clean stop status just after having been launched.
It gives a clear distinction between user triggered stop and failure
cancellation.
Merge pull request #79 from stephanedaviet/IDEX-1379

Fix IDEX-1379 Ability to stop run earlier