LU-16623 tests: interop sanity-flr/202 sanity-pfl/15

LU-16623 tests: interop sanity-flr/202 sanity-pfl/15

Fix interop testing with sanity-flr test_202 and sanity-pfl test_15
to request a specific number of stripes instead of "-c -1", which
may not always allocate objects on all OSTs if they are full/busy.

Test-Parameters: trivial
Test-Parameters: testlist=sanity-flr env=ONLY=202 serverjob=lustre-master serverbuildno=4527
Test-Parameters: testlist=sanity-pfl env=ONLY=15 serverjob=lustre-master serverbuildno=4527

Fixes: ced540165e ("LU-16623 lod: handle object allocation consistently")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I1df9324d9d978e9253f7d4a433d85934c33ebbe5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53628
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Alex Deiter
Reviewed-by: Oleg Drokin <green@whamcloud.com>