sync: Continue job if some fetchs failed but force-broken is set

With --force-broken it continue to fetch other projects but nothing
is added in directory because it abort some lines later.

Change-Id: I32c4a4619b3028893dc4f98e8d4e5bc5c09adb27

subcmds/sync.py

@@ -393,7 +393,7 @@ later is required to fix a server side protocol bug.
       t.join()
 
     # If we saw an error, exit with code 1 so that other scripts can check.
-    if err_event.isSet():
+    if err_event.isSet() and not opt.force_broken:
       print('\nerror: Exited sync due to fetch errors', file=sys.stderr)
       sys.exit(1)