logind fails to start in environments without dbus, such as LXC containers or
servers. Add a startup condition to avoid the very noisy startup failure.
Part of #772700
Gbp-Pq: Topic debian
Gbp-Pq: Name Only-start-logind-if-dbus-is-installed.patch
Documentation=https://www.freedesktop.org/wiki/Software/systemd/multiseat
Wants=user.slice
After=nss-user-lookup.target user.slice
+ConditionPathExists=/lib/systemd/system/dbus.service
# Ask for the dbus socket.
Wants=dbus.socket