If better_exec() throws a subprocess.CalledProcessError then show the output to
the user as it likely contains useful information for solving the problem.
(Bitbake rev: 8a6424ed871c3cbacd21cae8bc801197f83d67a6)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>