py3: store exception variables for use outside except

In python3 exceptions aren't defined outside the except block. Leading
to 'UnboundLocalError: local variable 'e' referenced before assignment'
errors.

To work around this, store the local variable into one that will have a
longer life.

virtManager/connection.py

@@ -1439,7 +1439,8 @@ class vmmConnection(vmmGObject):
             self._tick(*args, **kwargs)
         except KeyboardInterrupt:
             raise
-        except Exception as e:
+        except Exception as err:
+            e = err
             pass
 
         if e is None: