workaround for jenkins bug https://issues.jenkins-ci.org/browse/JENKINS-14193

The jenkins maven builder cannot reference environment variables if it is set
by the EnvInject plugin at the prebuilder step.  However the maven builder CAN
reference variables when loaded from the build environment setup (wrapper) step.
The only problem is that gerrit-git-prep only runs in the prebuilder step
which occurs aftern a build environment step (wrapper).  We want the
maven-properties.sh script to run after gerrit-git-prep because the
it queries for git info. A workaround is to call gerrit-git-prep
inside of the maven-properties script so it will run in the correct order.

Change-Id: Ie0a72d8509f5f1453e027486285c2817dbc67eb5
Reviewed-on: https://review.openstack.org/36879
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins