bitbake/knotty: ensure we return non-zero exit code on Ctrl+C

bitbake/knotty: ensure we return non-zero exit code on Ctrl+C

If the user uses Ctrl+C to exit out of the build, then ensure we return
a non-zero exit code since the entire build was not completed
successfully.

If nothing else, this is useful to avoid continuing in the bitbake
wrapper script in OE-Core if the initial pseudo build is interrupted.

(Bitbake rev: c11eab7fa230f1fd5cc33589f3555b94e95f202d)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>