Fix it so build_job triggers a build

The build_job method would not trigger a build because it
would do a GET on the build URL rather than a POST.  Adding
a body causes it to do a POST.

Change-Id: Idf40e462f970122234f85b5d1d2e72d178b5b39f
Closes-Bug: 1177831
Merge "Fix it so build_job triggers a build"