Features:
+* when a start job for a device unit is queued, when systemd runs in a container, make it fail immediately instead of wait for all eternity
+
* port libmount hookup to use API's own inotify interface, as soon as that is table in libmount
* bash completion for busctl, to make it truly useful
* nspawn:
- bind mount read-only the cgroup tree higher than nspawn
- refuses to boot containers without /etc/machine-id (OK?), and with empty /etc/machine-id (not OK).
- - support taking a btrfs snapshot at startup and dropping it afterwards
- introduce machines.target to order after all nspawn instances
- systemd-nspawn@.service should fail if some nspawn arg is invalid, with Type=notify
- PID 1 doesn't apply nspawns devices cgroup policy