LU-14745 tests: ensure sanity/51d has enough objects

LU-14745 tests: ensure sanity/51d has enough objects

Ensure that sanity test_51d has precreated enough objects on the
OSTs for the tests to finish without running out.  Otherwise,
some OSTs may be skipped and skew the results.

Test-Parameters: trivial testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity env=ONLY=51d,ONLY_REPEAT=5 mdscount=2 mdtcount=4
Fixes: fd5c915eff ("LU-15282 tests: improve sanity test_51d coverage")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ifaf79173aa34fc7f3b3b1ad3d2876b65c16d1474
Reviewed-on: https://review.whamcloud.com/48086
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>