If the cooker receives a SIGTERM it currently hangs using 100% CPU,
This patch adds in an intercept for the event and puts the cooker into
shutdown mode allowing it to exit cleanly/safely and avoiding the hang.
(Bitbake rev: 00c22434123739b0819b31d7b1d353901a3e12da)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>