LU-15460 test: wait quota pool to be prepared

LU-15460 test: wait quota pool to be prepared

When one OST pool was created, the corresponding quota pool
could need more time to prepare after it was created, then
fail to check the info of the quota pool

Lustre-commit: 83dd308db59a9b95c1db5efa12ea5af22e9c8346
Lustre-change: https://review.whamcloud.com/46853

Test-Parameters: trivial
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Change-Id: Ibea33403639087f27e438d71c0e87fea5367bc3e
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51947
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>