docker-base: ignore return code of systemd-tmpfiles
Ignore the return code of the systemd-tmpfiles command because
at this point we have already removed the /etc/machine-id (8f3beac)
and all tmpfiles lines with %m in them will fail and cause a bad
return code. Example failure:
[/usr/lib/tmpfiles.d/systemd.conf:26] Failed to replace specifiers: /run/log/journal/%m