overlay-shiftfs-tests: race with systemd-tmpfiles

I see some failures on ovl-mkdir-xattrs.sh where:

  1105 00:40:55 ERROR| [stderr] + echo 'dir is /tmp/tmp.9GEeAFGs0M'
      1106 00:40:55 ERROR| [stderr] + mkdir -p /tmp/tmp.9GEeAFGs0M/l /tmp/tmp.9GEeAFGs0M/u /tmp/tmp.9GEeAFGs0M/w /tmp/tmp.9GEeAFGs0M/t
      1107 00:40:55 ERROR| [stderr] + mkdir /tmp/tmp.9GEeAFGs0M/l/dev
      1108 00:40:55 ERROR| [stderr] + mount -t overlay -o lowerdir=/tmp/tmp.9GEeAFGs0M/l,upperdir=/tmp/tmp.9GEeAFGs0M/u,workdir=/tmp/tmp.9GEeAFGs0M/w o /tmp/tmp.9GEeAFGs0M/t
      1109 00:40:55 ERROR| [stderr] mount: /tmp/tmp.9GEeAFGs0M/t: mount point does not exist.

At some other instances, the failure is at mkdir /tmp/XXXX/l/dev, meaning /tmp/XXXX/l or /tmp/XXXX/u is gone.

As this is being run on a recently started container, my bet is that systemd-tmpfiles setup is still running. This would be /lib/systemd/system/systemd-tmpfiles-setup.service. This calls systemd-tmpfiles --remove --create. The --remove on /tmp, will remove everything there.

One possible solution is not using /tmp/ for these tests.

Cascardo.