When initializing an ext4 filesystem, omit the large_dir and metadata_csum_seed flags

This (untested!) MR makes vmdb2 create images without the problematic issues explained in issue #69 (closed).

I have not tested this, as I don't use vmdb2 to create imaes for x86 systems and would have to scramble for a working minimum config... this should be seen, if anything, as a proof of concept ☺