Currently a SIGTERM to the UI process causes the UI simply to lock up.
By setting an exit flag, the waitEvent can raise a SIGINT, allowing the
UI to break out the event loop and exit. Currently this is results in a
traceback but that is more desirable than a hanging process.
(Bitbake rev: 0d12041eceeae6bba2034b04913bb13abd67bd15)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>