EX-2992 tests: add sleep to verify lamigo and lpurge params

EX-2992 tests: add sleep to verify lamigo and lpurge params

This patch improves verify_one_lamigo_param() and
verify_one_lpurge_param() in hot-pools.sh to try
more times while verifying lamigo and lpurge params
in case there is a latency time for the param(s)
to be updated.

Test-Parameters: trivial testlist=hot-pools \
env=HOT_POOLS_EXCEPT="56"
Test-Parameters: trivial clientdistro=el8.3 \
testlist=hot-pools env=HOT_POOLS_EXCEPT="56"
Test-Parameters: trivial clientdistro=sles15sp2 \
testlist=hot-pools env=HOT_POOLS_EXCEPT="56"
Test-Parameters: trivial testgroup=review-dne-part-2 \
env=SANITY_LFSCK_EXCEPT="30",HOT_POOLS_EXCEPT="56"

Lustre-change: https://review.whamcloud.com/43256
Lustre-commit: b465db8b9b99e217d175f31230d04e10a9a17906

Change-Id: I0f4818baa1c2cd87920ff3189461b45b53871e90
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/43529
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>