Autologin does not work with lightdm session

[fossfreedom]

Raised from here canonical/ubuntu-flavor-installer#47

LightDM doesnt appear to be catered for by this bit of code (?)

ubuntu-desktop-provision/packages/ubuntu_init/lib/src/services/xdg_identity_service.dart

Line 64 in b7f9272

.getProperty('org.freedesktop.Accounts.User', 'AutomaticLogin')

The GTK flavours apart from Ubuntu itself all use lightdm

N.B. LightDM autologin needs this bit of text to be added to the lightdm configuration file

/etc/lightdm/lightdm.conf <<
[SeatDefaults]
autologin-user=myuser