Ansible launcher: add private gearman function

OpenStack's Zuul's gear server is spending most of its time dealing
with function registration (800 nodes, 20k functions each).
Alleviate the pain by adding a private gearman function to register
functions en masse.  In preliminary testing, this causes function
registration to take 27% of the current time.

Change-Id: I0d2342cadca5e3d6d6c1964a119e0d50b0bcc548
3 files changed