Launch systemd service with KeyringMode=shared

This allows gdm to pass the LUKS password through to PAM.

The login keyring will now be unlocked automatically if autologin is
enabled!
1 job from unlock-keyring in 6 minutes and 31 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #140000
build-fedora

00:06:31