/distribution/beaker/setup: use curl instead of twill to add lab controllers

This makes it slightly more resilient if the web UI changes (for
example, twill apparently doesn't understand <button type="submit"/>).

Change-Id: Ib54799438eb8caf28c4957e5ae497072daafa5d0
Merge "/distribution/beaker/setup: use curl instead of twill to add lab controllers" into develop