generic/192: fix spurious timeout

generic/192: fix spurious timeout

I have a theory that when the nfs server that hosts the root fs for my
testing VMs gets backed up, it can take a while for path resolution and
loading of echo, cat, or tee to finish.  That delays the test enough to
result in:

  --- /tmp/fstests/tests/generic/192.out	2023-11-29 15:40:52.715517458 -0800
  +++ /var/tmp/fstests/generic/192.out.bad	2023-12-15 21:28:02.860000000 -0800
  @@ -1,5 +1,6 @@
   QA output created by 192
   sleep for 5 seconds
   test
  -delta1 is in range
  +delta1 has value of 12
  +delta1 is NOT in range 5 .. 7
   delta2 is in range

Therefore, invoke all these utilities with --help before the critical
section to make sure they're all in memory.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zorro Lang <zlang@kernel.org>