nanobsd: Add uname/gname to the spec

[jlduran]

Summary

Also include the default NanoBSD uname/gname in the specification file.

By default, NANO_DEF_UNAME and NANO_DEF_GNAME map to root and wheel
respectively.

[emaste]

I'm not a fan of the wrapping for things like this; IMO it's better to just let it exceed 80 cols, or build up a string to add to the metalog piece by piece, etc.

[jlduran]

Address suggestions:

• Do not wrap strings

[imp]

I'm agnostic on the wrapping... I tend to use a 120ish limit myself, though I know that drives people nuts. Others in the project regularly commit > 80 < 100 lines and have for ~decades. kib is the only one that's still objecting.