/run/systemd/journal/dev-log but journald offers both:
- a native journal API at /run/systemd/journal/socket (see sd_journal_print(4))
- /run/systemd/journal/stdout for connecting a program's output to the journal
  (see systemd-cat(1)).

In addition to systemd-cat, the stdout access is required for nested container
(eg, LXD) logs to show up in the host. Interestingly, systemd-cat and LXD
containers require 'r' in addtion to 'w' to work. journald does not allow
reading log entries from this socket so the access is deemed safe.

Signed-off-by: Jamie Strandboge <jamie@canonical.com>