Change for the GEC8 demo: allow disk_image tags like this:
Change for the GEC8 demo: allow disk_image tags like this:

<disk_image
   name="urn:publicid:IDN+emulab.net+image+GeniSlices//UBUNTU91-LAMP" />

In other words, allow "GeniSlices" for the project, so we can add
images to be used from the rspec.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome