LU-11170 tests: add debugging to sanity/415

LU-11170 tests: add debugging to sanity/415

Add a loop of renames without the concurrent 'touch' operation to
measure the test time, and then a second loop that has the 'touch'
so that we can see whether slow renames are because of COS (which
would make the test failure a kernel bug to be fixed), or because
the test is running in a VM and the server/disk is slow (which is
something to be fixed in the test (e.g. by making "slow" relative
to the non-touch baseline time).

Lustre-change: https://review.whamcloud.com/49724
Lustre-commit: 6594babc73851fab335c514cd1fee018425e7bb3

Test-Parameters: trivial testlist=sanity env=ONLY=415,ONLY_REPEAT=120 mdscount=2 mdtcount=4
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ic1a952be0b861005b46da3e673216e455f3ebbe5
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Alex Deiter <alex.deiter@gmail.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/50203
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>