Disable fix-attrs and set S6_BEHAVIOUR_IF_STAGE2_FAILS

See merge request !1

This version does *not* attempt to run the initial fix-attrs stage,
and sets up /var/run/s6/services/* directories with a trick: the
"run" script is replaced by a symbolic link to /etc/services.d/<service>/run.

This trick works around the issue where we can't have a directory
that is both writable *and* where we can execute files: this is on
purpose, podman mounts all tmpfs dirs as noexec no matter how hard
you try (and it's a good thing from a security perspective).