xfsqa: define resblks for tests near ENOSPC

xfsqa: define resblks for tests near ENOSPC

Several tests assume a certain amount of disk space free after the
reserve block pool is filled. Changing the default size of the
reserve block pool breaks these tests because there is less space
available that first thought.

Change these tests to specify a known reserve block pool size of
1024 blocks to ensure that they continue to work correctly even if
the default size changes.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>