ci-master apt source not found on first run through image builder

The first time a ticket goes through the system, the ci-master ppa will have no packages in it. So when the imagebuilder is told to add ci-master and the ci-pool ppa, there will be a 404 error when it runs apt-get update because ci-master is so far uninitialized. We should find a way to either pre-init the ppa, or check it before handing it in a list to image-builder or check it in the image builder before trying to use it. My preference would be for #1 so that we have a clean slate to work from, but we definitely shouldn't just ignore the error from apt-get update since this could hide other problems and make them harder to debug.