doc/schema: Support iqn for storage pools

iSCSI qualified names (iqn) from RFC3721 may contain colons (':'), which
neither matches the absFilePath nor genericName:

 $ virsh pool-dumpxml myiscsipool
 <pool type='iscsi'>
 ...
   <source>
 ...
     <device path='iqn.2003-01.org.linux-iscsi.phahn-sid93.x8664:sn.8a3daa0d4efd'/>
   </source>
 ...
 </pool>

Add IscsiQualifiedName type and allow its use in sourceiscsi.
Signed-off-by: NPhilipp Hahn <hahn@univention.de>

docs/schemas/storagepool.rng

@@ -231,6 +231,7 @@
         <choice>
           <ref name='absFilePath'/>
           <ref name='genericName'/>
+          <ref name='IscsiQualifiedName'/>
         </choice>
       </attribute>
       <choice>
@@ -492,7 +493,6 @@
       <optional>
         <ref name='sourceinfovendor'/>
       </optional>
-
     </element>
   </define>
 
@@ -519,6 +519,12 @@
     </element>
   </define>
 
+  <define name='IscsiQualifiedName'>
+    <data type='string'>
+      <param name="pattern">iqn\.[0-9]{4}-(0[1-9]|1[0-2])\.[a-zA-Z0-9\.\-]+(:.+)?</param>
+    </data>
+  </define>
+
   <define name="PortNumber">
     <data type="short">
       <param name="minInclusive">-1</param>