Install Maven (and other similar Jenkins-required tooling) via Groovy scripts

[bleggett]

Right now we install maven on the Jenkins host box ourselves, but this has the downside of

• requiring a Chef cookbook
• because Jenkins is a fussy all-encompassing blob, the Jenkins UI doesn't think maven is installed (even though it's in the PATH) because we didn't install it thru Jenkins itself, as shown here: https://gist.github.com/tszpinda/53e958cf80b0f532c787

Propose we change our manually-installed Jenkins add-ons like Maven to be installed via this method, as it will simplify our installer and make Jenkins happy.