Feanil/admin plugins

@jarv @e0d @fredsmith @hkim823 

Updates to the jenkins role to not re-build plugins if they are already installed.  It also simplifies the admin jenkins role and speeds up re-runs of the jenkins roles in general.

@jzoldak @benpatterson FYI
Yes, because we are using the registered results of the download task.  Each item in the download task has its own results which contain the original item they were run with.