LU-7631 tests: wait_osts_up waits for MDS precreates

LU-7631 tests: wait_osts_up waits for MDS precreates

Fix wait_osts_up() to wait for the MDS to finish orphan cleanup and
precreate some OST objects so that there isn't a race to get all of
the OSTs available for conf-sanity test_82a.

Backport from master (2.12) branch to b2_10:
Lustre-change: https://review.whamcloud.com/#/c/27441/
Lustre-commit: edb0fb241bb5e0cc95c240ed977abf7f234ee045

Test-Parameters: trivial testlist=replay-single,replay-single
Test-Parameters: testlist=conf-sanity,conf-sanity,conf-sanity
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I534f0a1f36c3d00f702684041bfa991a4a3ebbe5
Reviewed-on: https://review.whamcloud.com/27441
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
(cherry picked from commit edb0fb241bb5e0cc95c240ed977abf7f234ee045)
Reviewed-on: https://review.whamcloud.com/33690
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>