Bug fix #529: Kill all Kimchi processes when stopping kimchid service

When using "tree.mount(); engine.start(); engine.block()" to start cherrypy
server, we need to manually subscribe to the signal handlers plugin.

For reference: https://cherrypy.readthedocs.org/en/3.2.6/refman/process/plugins/signalhandler.html

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>