Bug 107250

This bug was originally filed in:
- https://gitlab.gnome.org/GNOME/gnome-shell/issues/415

Environment:
- gnome-shell-3.28
- accountsservice-0.6.49

Description:

Log into a multi user system you will find the "Switch User" sub-menu of SystemIndicator(upper right corner of gnome-shell) is missing.

But it can be activated when:
- A new user is created via g-c-c but it will disappear after a reboot or relogin
- The gsettings value of "disable-user-swithching" is turned on then off
- Lock then unlock the screen

My findings:

I added some `print` sentences for gnome-shell and found that the default value of `_userManager.can_switch()` in `systemActions.js` (on a multi user system) is false while it should be true. Then I tried to downgrade `libaccountsservice` from `0.6.49` to `0.6.45` and the issue is resolved.

The version bump of `libaccountsservice` brings in some changes which causes this issue

suspected commit:
- The default behavior of act_user_manager_get_default() was changed by:
  [lib: only track users after act_user_manager_list_users](https://cgit.freedesktop.org/accountsservice/commit/?id=cd83d3d6fd5059b2e5283707c30f4af972631644)

Downstream bugs:
- [brc#1576903 Switch User menu item is missing](https://bugzilla.redhat.com/show_bug.cgi?id=1576903)
- [brc#1597350 - Switch User is missing in System Menu ](https://bugzilla.redhat.com/show_bug.cgi?id=1597350)
- [boo#1100041 - The "switch user" disappeared from control center on Tumbleweed gnome](https://bugzilla.opensuse.org/show_bug.cgi?id=1100041)