make-release: Create output directory if needed
Automatically create the --dir directory if it does not already exist,
which makes this script slightly easier to use. Remove the now
uneeded mkdir from the top-level makefile.
Change-Id: I1f4561120a70263b0b2b194e65fec55fb5666f40
Reviewed-on: https://gerrit.openafs.org/14115
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>