Add devstack-trusty-dib image.

Add a new devstack trusty image to nodepool that is built via dib on the
nodepool server. This is our first test of the new dib features added to
nodepool. Once we have these images in glance and are able to boot nodes
off of them we can add new tests that check their behavior.

Change-Id: I179df9117be538c3ab44cce3a3cd579e03e21e90
Merge "Add devstack-trusty-dib image."