LU-18646 tests: use /dev/urandom to consume space

LU-18646 tests: use /dev/urandom to consume space

It appears newer ZFS is using data compression by default, so reading
from /dev/zero results in files not consuming the expected amount of
space.  Instead, read from /dev/urandom for ZFS to write files in
sanity-quota and ost-pools to ensure they fill the OSTs as expected.

Minor script style cleanups for affected tests.

Test-Parameters: trivial testlist=sanity-quota,ost-pools fstype=zfs
Test-Parameters: testlist=sanity-quota,ost-pools fstype=ldiskfs
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ia2340da6e4c6d00123078545fde135a89c2540e5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57871
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Sergey Cheremencev <scherementsev@ddn.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>