contint: split Zuul server and merger

Puppet work to upgrade Zuul to a version that factors out the
preparation of git merges to gearman workers (known as zuul-merger).

Adds git-daemon on the labs instance and configure the Zuul url to
localhost.

Tested on labs.

Change-Id: Id88f1e3ee47ea2dac673257c8cc901c314170076
Merge "contint: split Zuul server and merger" into production