[Xen-API] Fix the rtc/timeoffset entry.

It cannot be 'None' as this is not parseable by the Java xmlrpc
library.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>

tools/python/xen/xend/XendDomainInfo.py

@@ -867,7 +867,10 @@ class XendDomainInfo:
 
         # convert two lists into a python dictionary
         vm_details = dict(zip(cfg_vm, vm_details))
-        
+
+        if vm_details['rtc/timeoffset'] == None:
+            vm_details['rtc/timeoffset'] = "0"
+
         for arg, val in vm_details.items():
             if arg in XendConfig.LEGACY_CFG_TO_XENAPI_CFG:
                 xapiarg = XendConfig.LEGACY_CFG_TO_XENAPI_CFG[arg]