LU-14094 tests: improve sanity.sh test_311

LU-14094 tests: improve sanity.sh test_311

Improve sanity.sh test_311 to see why the number of the objects
doesn't decrease as expected.

Test-Parameters: trivial testlist=sanity env=ONLY=311,ONLY_REPEAT=200
Test-Parameters: trivial testlist=sanity env=ONLY=311,ONLY_REPEAT=200
Test-Parameters: trivial testlist=sanity env=ONLY=311,ONLY_REPEAT=200
Test-Parameters: trivial testlist=sanity env=ONLY=311,ONLY_REPEAT=200
Test-Parameters: trivial testlist=sanity env=ONLY=311,ONLY_REPEAT=200
Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: Iabbaed42c5654ef31bc9f98fe9868785f8ff2f18
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55566
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>