launchdaemon support for MacOS

launchdaemon support for MacOS

the changes needed to switch from a StartupItem to a LaunchDaemon for
the MacOS OpenAFS client

Change-Id: I4c113d232186eaa06bd6793a5fd151053bf91efe
Reviewed-on: http://gerrit.openafs.org/564
Tested-by: Claudio Bisegni <Claudio.Bisegni@lnf.infn.it>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Claudio Bisegni <Claudio.Bisegni@lnf.infn.it>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-on: http://gerrit.openafs.org/966