ext4: regression test for a ENOSPC warning

ext4: regression test for a ENOSPC warning

This adds a regression test for a ENOSPC warning which can be
triggered if '-odioread_nolock,nodelalloc' and quota are used.

The bug was fixed by patch

"Ext4: fix ENOSPC when both quota and dioread_nolock are enabled".

[Eryu: add comments on using syncfs instead of sync]

Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>