Update jenkins jobs to optionally allow trusty

Now that zuul is selecting the node label for all jobs we can make
trusty an option for all dsvm jobs. A subsequent change will update zuul
to select trusty nodes. We are staggering the changes to avoid races
between zuul and jenkins config updates.

Change-Id: If3abb111f9378c192e647ceaced5bc9b16fe6bb4
Merge "Update jenkins jobs to optionally allow trusty"