conf: fix domaincommon.rng to accept network name with quotes

The network name is currently of type "deviceName" but it should be
"text" as name is defined in the network.rng.
Signed-off-by: NShivaprasad G Bhat <sbhat@linux.vnet.ibm.com>

docs/schemas/domaincommon.rng

@@ -2065,7 +2065,7 @@
           <interleave>
             <element name="source">
               <attribute name="network">
-                <ref name="deviceName"/>
+                <text/>
               </attribute>
               <optional>
                 <attribute name="portgroup">