tests: fix race in dirrem01 and dirrem02

tests: fix race in dirrem01 and dirrem02

Previously the '--checkpoint-action=echo' was triggered after
'--checkpoint-action=sleep=1' - so the order of events *usually*
was (for --format='gnu'):

  ...
  1. checkpoint handler before write of 'dir/sub' member
  2. one-second delay
  3. stderr write: 'tar: Write checkpoint 3'
  4. write the member 'dir/sub' into the archive
  5. check that the member's ctime has not been changed
  6. genfile's detecting 'Write checkpoint', doing unlink
  ...

But sometimes, the genfile was fast enough to win the race and
unlinked the directory before the member was written into the
archive (IOW, the order was 1-2-3-6-4-5).  This led to the
occasional warning 'tar: dir/sub: file changed as we read it'.

Swap the order of 'sleep=1' and 'echo' actions so the genfile
utility has (hopefully) enough time to do the unlink before
writing the file into the archive (enforce 1-2-3-6-4-5 order).

* tests/dirrem01.at: Swap 'sleep=1' and 'echo' actions.
* tests/dirrem02.at: Likewise.