If DISPLAY wasn't set, launching hob has printed a traceback
difficult to understand. Now, the exception is caught and it
shows a human message.
[YOCTO #2596]
(Bitbake rev: a41098a2dacbd903422ccdcd1885b0f351c7ddf3)
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>