Add a testcase for DBusActivatable=true

Add a fairly realistic testcase that ensures that GDesktopAppInfo with
DBusActivatable=true can successfully talk to GApplication for a variety
of purposes.

https://bugzilla.gnome.org/show_bug.cgi?id=699259

gio/tests/.gitignore

@@ -13,6 +13,7 @@ converter-stream
 credentials
 data-input-stream
 data-output-stream
+dbus-appinfo
 de/
 desktop-app-info
 echo-server