Alter the schema to allow a VxHS block device. Sample XML is:

  <disk type='network' device='disk'>
    <driver name='qemu' type='raw' cache='none'/>
    <source protocol='vxhs' name='eb90327c-8302-4725-9e1b-4e85ed4dc251'>
      <host name='192.168.0.1' port='9999'/>
    </source>
    <target dev='vda' bus='virtio'/>
    <serial>eb90327c-8302-4725-9e1b-4e85ed4dc251</serial>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
  </disk>

Update the html docs to describe the capability for VxHS.

Alter the qemuxml2xmltest to validate the formatting.
Signed-off-by: NAshish Mittal <Ashish.Mittal@veritas.com>
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>