CA-141526: Putting VBD path to /dev/xvdX for HVM guests

/dev/hda is anyways meaningless for HVM guest.So, we always populate the
VBD path to be /dev/xvdX.
Signed-off-by: Ravi Pandey <ravi.pandey@citrix.com>
Merge pull request #1921 from ravippandey/CA-141526

CA-141526: Putting VBD path to /dev/xvdX for HVM guests