Setup tooling and jobs for openstack Gerrit ver 2.8 and beyond

Previous versions of Gerrit used maven as the build tool, it has since
switched to use buck. I believe the switch happened in ver 2.7.  We are
now hosting a fork of Gerrit ver 2.8 so we need to setup tooling and
jobs to build newer versions of gerrit.  This patch sets up tooling and
jobs required for building the openstack Gerrit ver 2.8.  We now have
two sets of jenkins jobs to build gerrit, one for Gerrit prior to ver
2.4.x (maven) and one for Gerrit post ver 2.7 (buck).

Notes:
1. Buck does not have OS packages for easy installation so it needs to
be built from source using ant (requires gcc as well).
2. Maven jobs execute only when commits are made to 2.4.x branch.
3. Buck jobs execute when commits are made to branches other than 2.4.x
4. The origin post job 'gerrit-package' now publishes artifacts to
tarballs.o.o/ci/gerrit instead of tarballs.o.o/ci
5. Buck requires the zip package to build gerrit.
6. Buck and gerrit clones need to be at same directory level

Partial-Bug: #1082781
Change-Id: I1de9f127fa6826fb0a686d12dc77c0edff34be7c
Merge "Setup tooling and jobs for openstack Gerrit ver 2.8 and beyond"