Add a script to test the Jenkins API.

Using the extended versions of python-jenkins that are used
by Zuul and devstack-gate, exercise all of the Jenkins API
calls that are used by by Zuul, devstack-gate, and Jenkins
Job Builder.

(JJB doesn't need any extended methods.  The extended methods
used by devstack-gate have been upstreamed, but not released.)

Change-Id: I9c3a4d7cfc96965ceb83b8c5ea4b12d4f2e07e12
Reviewed-on: https://review.openstack.org/22580
Reviewed-by: Paul Belanger <paul.belanger@polybeacon.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins