LU-9332 tests: fix pool_list issue in conf-sanity test_82b

LU-9332 tests: fix pool_list issue in conf-sanity test_82b

In conf-sanity.sh test_82b, if we use separated MGS and MDS nodes,
MDS needs more time to list the OSTs in pool, so use wait_update
instead of the pool_list command.

Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: I8f7281d44a12731d7ae2d1f8fa9bad163086cecc
Reviewed-on: https://review.whamcloud.com/26582
Tested-by: Jenkins
Reviewed-by: Parinay Kondekar <parinay.kondekar@seagate.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>