Ensure we capture stderr, always write the output to the log, and don't be so
emotional in the warning message.
(From OE-Core rev: 87110e971c548d9d3eb7296ea6772d18e0226e53)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>