conf: Fix XML formatting of RNG device info

https://bugzilla.redhat.com/show_bug.cgi?id=1035118

When outputting the XML for the RNG device, the code didn't format the
PCI address info. Additionally the schema wasn't expecting the info
although it was being parsed and used internally. Fix those mistakes and
add test for the PCI info section.

docs/schemas/domaincommon.rng

@@ -3956,6 +3956,12 @@
         <optional>
           <ref name="rng-rate"/>
         </optional>
+        <optional>
+          <ref name="alias"/>
+        </optional>
+        <optional>
+          <ref name="address"/>
+        </optional>
       </interleave>
     </element>
   </define>