There is a final solution for setting system and user-wide umask in OS X Yosemite 10.10.3:
instead of user-wide /etc/launchctl-user.conf
use:
launchctl config user umask 002
(example umask for setting 775 permissions)
instead of system-wide /etc/launchctl.conf
use:
launchctl config system umask 002
(example umask for setting 775 permissions)
Apple published the how-to for "Yosemite umask problem" update five days ago (Apr 8, 2015) here.