Code review comment for ~dbungert/curtin:nonzero-fs_pass

We discussed this internally a bit and still think we should change the default. (I haven't heard back from the MAAS team yet). The kernel is not the only thing that reads filesystems (UEFI firmware and grub both do), and for the filesystems that do not implement any kind of non-trivial fsck, we're not at the boot optimization point where adding an invocation of essentially /bin/true will have a noticeable impact. So the (small) upsides seem to outweigh the (even smaller) downsides and I don't think this makes enough difference to anyone to warrant a feature flag.