block/vxhs.c: Add qemu-iotests for new block device type "vxhs"

These changes use a vxhs test server that is a part of the following
repository:
https://github.com/VeritasHyperScale/libqnio.git



Signed-off-by: Ashish Mittal <Ashish.Mittal@veritas.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Message-id: 1491277689-24949-3-git-send-email-Ashish.Mittal@veritas.com