mkfs.ufs support

[cschech]

It would be an excellent addition to add UFS support to growlight, which would open the door to clean BSD installs from scratch on Linux straight from original source distributions (rather than self-hosted in installers running random upstream BSD kernels).

I will try to work on this in a branch and submit back a pull request. Worthwhile?

[dankamongmen]

agreed, this ought be easy enough