domain: We can't always release handle if undefining, fix another way

src/virtManager/connection.py

@@ -751,6 +751,7 @@ class vmmConnection(vmmGObject):
     def rename_vm(self, domainobj, origxml, newxml):
         # Undefine old domain
         domainobj.delete()
+        domainobj.release_handle()
 
         newobj = None
         try:

src/virtManager/domain.py

@@ -1116,8 +1116,7 @@ class vmmDomain(vmmDomainBase):
 
     def delete(self):
         self._backend.undefine()
-        del(self._backend)
-        self._backend = None
+        # XXX: If want to release domain here, fix connection polling
 
     def resume(self):
         if self.get_cloning():