Code review comment for lp:~javier.collado/utah/preseed_tests

This branch got a little bit old, so I rebased the changes to make them easier to merge.

Max, I know it's a big change, but it just adds testcases and documentation. If you want to run them, please try the following:

$ nosetests --with-doctest utah/preseed.py tests/
..................................................
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Ran 50 tests in 0.022s

OK