Remove support for floppy disks in Nova for OpenStack Compute (nova)

Background ------------------ The "VENOM" vulnerability (CVE-2015-3456)[1] was caused due to a Floppy Disk Controller (FDC) was being initialized for all x86 guests, regardless of their configuration — so even if a guest does not explicitly have a virtual floppy disk configured and attached, this issue is exploitab...