ext4: regression test for wrong assert in ext4_mb_normalize_request()

ext4: regression test for wrong assert in ext4_mb_normalize_request()

Regression test for:
    b5b6077 ext4: fix wrong assert in ext4_mb_normalize_request()

Meanwhile make minor changes to _scratch_mkfs_ext4() in common/rc,
_scratch_mkfs_ext4() might fail due to conflicts between being passed options
and MKFS_OPTIONS. We fix this by ignoring MKFS_OPTIONS if it fails the first
time(see _scratch_mkfs_xfs()), as suggested by Lukas Czerner.

[dchinner: converted to use xfs_io]

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>