Documentation fixes

There are three doc fixes for builders.py  in this change.

Link to Gradle plugin fixed
Maven-target example has been fixed
Copyartifact docs cleaned up

Change-Id: Ie50e94ace2041735cc986eb117597262b40b0fa5
Reviewed-on: https://review.openstack.org/25962
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins
Add support for the MultiJob plugin

Change-Id: Ie6c06072eae17fddf241fa0bc416d20c9a2248dc
Reviewed-on: https://review.openstack.org/26321
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