gnome-shell-perf-tool: Fix various problems

* Fix wrong parameter name to on_name_appeared callbacks
* optparse doesn't just leave extra command line arguments, it
  errors out, so don't try to pass through extra arguments -
  instead add explicit passthrough for '--replace'
* Fix usage of Gio.DBusProxy
* Add a default value for --perf so that if it's not supplied
  things don't die with a mysterious error message. (This wasn't
  needed when --perf enabled perf-mode)

https://bugzilla.gnome.org/show_bug.cgi?id=687287