- add a restart option to restart without touching the ioloop (for unit tests)
- cleaning some old callback options
savepoint
removed prints
fixed the protected call
Merge remote-tracking branch 'refs/remotes/mozilla/thefab-async_experiment' into async_experiment

Conflicts:
	circus/util.py
make sure _exclusive_running_command is set back to None on error
move the exception checking of a future to circus/util.py
fix (add_job doesn't exist anymore)
fix a synchronized issue
removing debug
better way for starting/stopping arbiter (if the loop is provided during arbiter.__init__(), the loop is not started/stopped by the start/stop method)
better start/stop process (and fix restart issues)
test_stream is now async compliant (and pass)
start to fix reload_from_config (not ended)
Merge remote-tracking branch 'refs/remotes/mozilla/thefab-async_experiment' into async_experiment

Conflicts:
	circus/tests/test_arbiter.py
	circus/util.py
Merge branch 'async_experiment' of https://github.com/thefab/circus into async_experiment