LU-16296 tests: sanity-flr/36c to save on writes

LU-16296 tests: sanity-flr/36c to save on writes

there is no need to write 600MB as this may take significant
time if used with HDD.

Test-Parameters: trivial testlist=sanity-flr
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ic6001aaba7f349a14ade1c720d175430370dd7e9
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49025
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>