xfs: test mkfs min log size calculation w/ rt volumes

xfs: test mkfs min log size calculation w/ rt volumes

In "mkfs: set required parts of the realtime geometry before computing
log geometry" we made sure that mkfs set up enough of the fs geometry to
compute the minimum xfs log size correctly when formatting the
filesystem.  This is the regression test for that issue.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>