bitbake: fetch2: make fetch failure errors more readable

bitbake: fetch2: make fetch failure errors more readable

Most of the time we don't need to see the fetch command; the fetch log
includes the command as a debug message in any case, so omit it. Also
adjust the way command output is printed (we don't need stderr/stdout
labelled, and print "no output" instead of "output:\nNone" when there is
no output.

(Bitbake rev: a75505a52e4da918222100221f79e8a658f90446)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>