Fix tests to run on OpenBSD

  Use a hardcoded sequence for there's no seq(1) in OpenBSD.

  awk(1) doesn't support interval regular expression syntax ({n,m})
  on some BSDs.

  hostname(1) has no -f flag on OpenBSD and. Try it first and
  fallback to `uname -n`.

  Omit explicit template in mktemp(1) call.