Add support for simple rollbacks during `podman auto-update`. Rollbacks
are enabled by default. If a systemd unit cannot be restarted after an
update, the previous image will be retagged and the unit will be
restarted a second time.
Add system tests for rollbacks. Also fix a bug in the restart sequence;
we have to use the channel to actually know whether the restart was
successful or not.
NOTE: To make rollbacks really useful, users must run their containers
with `--sdnotify=container` such that the containers send the ready
message over the (mounted) socket. This way, restarting the systemd
units during auto update will block until the message has been received
(or a timeout kicked in).
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>
30df551bde