LU-16904 tests: Fix sanity test 248c and 360 when PFL layout is used

LU-16904 tests: Fix sanity test 248c and 360 when PFL layout is used

For 248c, use stripe counct 1 for root before the readahead issue described
in LU-17755 and LU-15155 get fixed
For 360, use stripe count 1 for test dir to make sure the files created under
it have object greater than 1M on single OST to test delayed iput

Test-Parameters: trivial
Test-Parameters: testlist=sanity env=fs_STRIPEPARAMS="-E 1M -c1 -E eof" env=ONLY="248c,360"
Test-Parameters: testlist=sanity env=fs_STRIPEPARAMS="-E 64k -c 1 -E eof" env=ONLY="248c,360"
Test-Parameters: testlist=sanity env=fs_STRIPEPARAMS="-E 64k -c 1 -E eof -c 2" env=ONLY="248c,360"
Test-Parameters: testlist=sanity env=fs_STRIPEPARAMS="-E 64k -c 1 -E 1M -c 2 -E eof -c 4 -S 4M" env=ONLY="248c,360"

Signed-off-by: Wei Liu <sarah@whamcloud.com>
Change-Id: I93341001714c5d0942f2f8f2895ca8bb545dc344
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54918
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Patrick Farrell <patrick.farrell@oracle.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>