connection: Fix race when updating conn.vms

We update the canonical conn.vms list in an idle callback, so any parts
of the main UI thread won't see the conn.vms change while they are
iterating over it.

Problem with this, is that if multiple ticks() are scheduled before
the first idle handler has a chance to run, we can overwrite the VM
list can fail to be correctly updated.

Fix this by only updating 'vms' if it actually changed.

virtManager/connection.py

@@ -1160,11 +1160,16 @@ class vmmConnection(vmmGObject):
             if not self._backend.is_open():
                 return
 
-            self.vms = vms
-            self.nodedevs = nodedevs
-            self.interfaces = interfaces
-            self.pools = pools
-            self.nets = nets
+            if pollvm:
+                self.vms = vms
+            if pollnet:
+                self.nets = nets
+            if polliface:
+                self.interfaces = interfaces
+            if pollpool:
+                self.pools = pools
+            if pollnodedev:
+                self.nodedevs = nodedevs
 
             # Make sure device polling is setup
             if not self.netdev_initialized: