Use the haproxy source balance method.

* modules/cgit/manifests/init.pp: HTTP(S) access to the git cluster may
end up making connections to different node members potentially causing
fetches to fail when a ref is visible on one node but not on another.
Fix this by using the source balance method. Every request from a single
host will be served by one backend node unless nodes are added or
removed.

Change-Id: Iedca1938277020b837eb1607e43013f5feb2ed2d
Merge "Use the haproxy source balance method."