reproducible: Allow configuration of saved debug output
If OEQA_DEBUGGING_SAVED_OUTPUT is set in the environment, use this location
to store reproducibile build failure output. This aids debugging on the
YP autobuilder in particular.
Use a date in the directory name to make it easier to find failure output.
Also clean up empty directories as they're unnecessary distracting noise.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
