lib/oeqa/utils: qemurunner: fix when runqemu errors out

lib/oeqa/utils: qemurunner: fix when runqemu errors out

When qemu doesn't start or runqemu errors out
(some wrong option passed or sudo needs a password for setting tap) we
want to display the output but oe-core commit 9de7fe11967576f4a8b24e653c6b9a02e5f6d85b/
poky commit 51588936d4a8cde3c9bb05800240c0a0f5dedf8d
changed the kill method and broke this code, so let's fix it.

(From OE-Core rev: 923d4bd548911caa0b419c10905895af1e8e7026)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>