Make gerrit git replica and jeepyb paths configurable

* Gerrit: make the path to the local replica configurable
  (default to /var/lib/git)
* Set the local replica path on review-dev to /opt/lib/git
* Gerrit: make the jeepyb cache dir configurable
  (default to /opt/lib/jeepyb)

Change-Id: I9b94fa540bb400abcc746c5c962bb3b5e2b372e3
Merge "Make gerrit git replica and jeepyb paths configurable"