stderr would previously be appended to stdout, corrupting the result when something...

stderr would previously be appended to stdout, corrupting the result when something was outputed to stderr but exit code was still 0 (non-fatal warning messages). This commit makes the code parse only stdout, but output stderr if an error happened.

(Bitbake rev: 4a480a052f450c4ee061ab0e60a495a45f140cf9)

Signed-off-by: Adrien Bustany <adrien.bustany@nokia.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>