Exit gracefully if we are disabled systemwide
Sysadmins might want to disable any kind of initial setup for their users, perhaps because they pre-configure their environments. We should provide an easy way to do it.
At least the anaconda installer provides an option to skip any kind post-install setup tools so, for now we're only adding support for that but more might be added in the future.
https://bugzilla.gnome.org/show_bug.cgi?id=777707
This is a downstream patch that we've been carrying in Fedora for a while that @rtcm did a long time ago. I talked to @wjt today and he suggested I submit it upstream; here it is. I've updated it a bit to build after the gis_ensure_stamp_files() API change in .91.1 and changed it to use g_autoptr as the rest of the code base has been updated to do that as well.