deploy gerrit plugins into folder with plugin name

This change deploys built gerrit plugins into
http://tarballs.openstack.org/ci/gerrit/plugins/$PLUGIN_NAME
This will provide a known location to look for the plugin in downstream
obs so we can automate the download and installation of the plugin.

Change-Id: Icfcd9aa932313c0620ebeb5c8104771675d88db1
Merge "deploy gerrit plugins into folder with plugin name"