fix: extraction of module UI

The cluster leader keeps a copy of UI code. During the module update the
previous UI code is renamed before being deleted. If an error occurs it
is ignored in this case.

core/imageroot/var/lib/nethserver/cluster/actions/update-module/50update

@@ -139,7 +139,11 @@ for idx, retval in enumerate(update_retvals):
         agent.run_helper('extract-ui', image_url).check_returncode()
         # Replace the app UI directory. Cannot find a way to do this
         # atomically and faster.
-        os.rename(appspath + mid, appspath + mid + dsfx + '~')
+        try:
+            os.rename(appspath + mid, appspath + mid + dsfx + '~')
+        except Exception as ex:
+            print(agent.SD_WARNING + f"Cannot rename the old {mid} UI directory:", ex, file=sys.stderr)
+            pass # ignore errors if the source dir is missing
         os.rename(appspath + mid + dsfx, appspath + mid)
         agent.run_helper('rm', '-rf', appspath + mid + dsfx + '~')
         # Remove the previous image, we do not need anymore