Currently if this fails you see:
"AssertionError: 1 != 0"
which is useless. Add the output of the failed command so we can stand
some chance of debugging what went wrong.
(From OE-Core rev: e482f9bfddc6b710c9b566c3d3433dc2d7d5a22e)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>