bitbake: knotty: Implement console 'keepalive' output

bitbake: knotty: Implement console 'keepalive' output

CI systems like jenkins and buildbot will timeout applications which haven't had console output
in some period of time. Add 'keepalive' output to knotty which gives output every 5000s if not
other output was made and tasks are still running. This reduces some problems encountered
with our CI testing.

(Bitbake rev: aa4f31e5741dd98acec73f16f6028e52f4c22d6f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>