EX-8780 test: wait osts up after restart

EX-8780 test: wait osts up after restart

In test_18e of sanity-lfsck, the OSTs could not be ready on all MDTs
and the LFSCK status will be incorrect because the LFSCK notify can
not be sent to all OSTs.

Change-Id: If1ed5d920d5c8b99d42f59f92a1e245a9e2a8267
Test-Parameters: trivial testlist=sanity-lfsck,sanity-lfsck,sanity-lfsck,sanity-lfsck,sanity-lfsck
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53531
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>