make Zuul query Jenkins directly

Zuul interacts with Jenkins via Jenkins HTTP interface. Until now we
have been using the public facing interface which has some drawbacks.
Zuul does not pipeline its requests, so on each action it has to
negotiate a SSL session and the request is passed via Apache proxying.

This change makes Zuul query Jenkins directly on 127.0.0.1 with HTTP,
that saves the time of the SSL negotiation and the overhead of Apache
proxying.

Change-Id: Ib6313abd651d1c826c495b0cc734ce650d7d9314