journal: when listing logs of a container make sure we don't accidentally show messages from host too
journald: cache cgroup root path, instead of querying it on every incoming log message
units: don't run readahead done timers in containers

We don't run the collector in the container either, hence we don't need
to stop it either.
journald: make sure the stdout/stderr stream fd is removed from epoll before we close it
sd-event: try to move each wakeup to the same spot within every 10s

In addition to the same spot within every 1min, every 1s, every 250s