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

vmdb/plugins/mkfs_plugin.py

@@ -51,6 +51,17 @@ class MkfsStepRunner(vmdb.StepRunnerInterface):
                 cmd.append("-L")
             cmd.append(label)
 
+        # Ext4 filesystem features large_dir and metadata_csum_seed
+        # are known to make versions of GRUB older than 2.06-8 unable
+        # to boot. Keep this around at least until it is no longer
+        # likely enough(?) users will try to build older target
+        # systems.
+        if fstype == "ext4":
+            cmd.append("-O")
+            cmd.append("^large_dir")
+            cmd.append("-O")
+            cmd.append("^metadata_csum_seed")
+
         options = values["options"] or None
         if options:
             for opt in options.split(" "):