qemu: Add qemu command line generation for a VxHS block device

qemu: Add qemu command line generation for a VxHS block device

The VxHS block device will only use the newer formatting options and
avoid the legacy URI syntax.

An excerpt for a sample QEMU command line is:

  -drive file.driver=vxhs,file.vdisk-id=eb90327c-8302-4725-9e1b-4e85ed4dc251,\
   file.server.type=tcp,file.server.host=192.168.0.1,\
   file.server.port=9999,format=raw,if=none,id=drive-virtio-disk0,cache=none \
  -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,\
   id=virtio-disk0

Update qemuxml2argvtest with a simple test.

Signed-off-by: Ashish Mittal <Ashish.Mittal@veritas.com>
Signed-off-by: John Ferlan <jferlan@redhat.com>