t/op/magic.t: handle busybox ps

t/op/magic.t: handle busybox ps

There were two problems here:

- busybox ps doesn't support the ps -p option and produces an error
  and fails when it sees it.  This does no harm beyond noise.
- busybox ps ignores a PID parameter, always producing a complete
  list of processes, so the like()s around line 430 would include the
  entire ps list in their NAME values, producing a bunch of noise that
  TEST (but not harness) chokes on.