graceful_shutdown_timeout sometimes doesn't work on python 2

[sileht]

When Service.terminate use time.sleep() signal.alarm doesn't work as expected on py27:

https://github.com/sileht/cotyledon/blob/master/cotyledon/__init__.py#L148-L150

https://github.com/sileht/cotyledon/blob/master/cotyledon/tests/test_cotyledon.py#L206-L208

Need to figure why and/or found a workaround.

[sileht]

Because of the signals implementation the current cotyledon code doesn't work as expected. Some times signals are lost because of https://bugs.python.org/issue5315 I have used time.sleep to mitigate the issue but it looks like not enought, for example ceilometer-collector doesn't stop on SIGTERM even have the shutdown timeout the SIGALRM handler is not called.