Add support for Qemu devices on cloud instances

This adds support to the server for running Qemu devices on cloud instances.  It should be merged before the accompanying changes to the gui are merged in.

You can test this together with the gns-125 branch in the gui repository.  The gns-125 branch in the gui is currently set to pull from the server gns-125 branch rather than dev.

You can find small (23MB) qemu images of Microcore linux on the gns community forum.  See the Appliances link on the Downloads page.  These are handy for testing with.