LU-10052 tests: wait for OST objects to be deleted

LU-10052 tests: wait for OST objects to be deleted

In test_20b of replay-single, the used space difference after
the file creation and deletion shows that a block is not freed,
wait for OST objects to be destroyed after recovery is done.

Test-Parameters: trivial testlist=replay-single.sh ostfilesystemtype=zfs mdtfilesystemtype=zfs
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Change-Id: I6311d8b8fa4cea713a9755cfb6a3d63e693c8344
Reviewed-on: https://review.whamcloud.com/30678
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>