schema: Add physical sizing element for storagevol grammar

https://bugzilla.redhat.com/show_bug.cgi?id=1572491

Commit id '78661cb1' added a physical output, but failed to update
the schema resulting in a failure from virt-xml-validate.

While at it - update the storagevolschemadata for the output.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
ACKed-by Michal Privoznik <mprivozn@redhat.com>

docs/schemas/storagevol.rng

@@ -56,6 +56,11 @@
           <ref name='scaledInteger'/>
         </element>
       </optional>
+      <optional>
+        <element name='physical'>
+          <ref name='scaledInteger'/>
+        </element>
+      </optional>
     </interleave>
   </define>
 

tests/storagevolschemadata/qcow2-no-source.xml

@@ -3,6 +3,7 @@
   <key>/var/lib/libvirt/images/OtherDemo.img</key>
   <capacity unit="G">5</capacity>
   <allocation>294912</allocation>
+  <physical unit="G">5</physical>
   <target>
     <path>/var/lib/libvirt/images/OtherDemo.img</path>
     <format type='qcow2'/>