LU-18293 test: use direct IO for quota test

LU-18293 test: use direct IO for quota test

In subtest 1b, 1c, 1d, the quota test should use DD with direct flag
to make sure the over-quota check is correct.

Test-Parameters: trivial testlist=sanity-quota env=ONLY=1,ONLY_REPEAT=100
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Change-Id: Ief327fb56fdd2e5911e5f57256d5ec683e5edf8e
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58533
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sergey Cheremencev <scherementsev@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>