Description of problem:

Especially with --csv output, there is a need to trace
domains across migrations, renames, etc. (or conversely
to distinguish domains over time that happened to have
the same name).

For this reason we should add a --uuid option to those tools
which produce output that could be parsed by a database,
currently only virt-df.

Version-Release number of selected component (if applicable):

libguestfs 1.5.23