macos: packaging support for MacOS X 10.12

macos: packaging support for MacOS X 10.12

This commit introduces the new set of changes / files required to
successfully create the dmg installer on OS X 10.12 "Sierra".

Reviewed-on: https://gerrit.openafs.org/12420
Reviewed-by: Joe Gorse <jhgorse@gmail.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 0bed87a15db11bccb693b3a54f704ee5751ae553)

Change-Id: I71a22e2ee43cb86ccdbe16c42b582d90adc91115
Reviewed-on: https://gerrit.openafs.org/12432
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Tested-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>