add Environment File Plugin

This commit adds the Environment File Plugin to JJB.
https://wiki.jenkins-ci.org/display/JENKINS/Envfile+Plugin

Change-Id: Id35a4d6ab25b0440303da02bb91007b459979243
Reviewed-on: https://review.openstack.org/35170
Reviewed-by: Arnaud Fabre <fabre.arnaud@gmail.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins