Create `log.dirs` directories in `_setup` recipe

Not really sure how I missed this before, because this feels like
something that should really be done, right?
Add integration tests for creating `log.dirs`
Merge branch 'create-log-dirs'
Version bump to v0.4.1

I’d consider this a patch release due to the fact that this should’ve
been done since the start, and I’m a bit surprised that no-one has filed
an issue about it. Suppose that’s because Kafka actually create the log
directories and then it’s not a big deal.
Convert _ALL_ configuration attributes to a flat namespace

Oh this is just the beginning. FULL SPEED AHEAD!
Put all configuration attributes under a `broker` namespace

Next stop, dynamically generate configuration properties.
Generate property keys from `broker` attributes

Instead of defining _ALL_ possible configuration attributes in
`attributes/default.rb` we’ll generate key-value pair from whatever
attributes that are found under the `broker` namespace.

The diffs in this commit are so _HORRIBLE_, but I couldn’t think of any
other way to get this done. There are still some tests that needs to be
rewritten / added, and I do believe that the configuration generation
creates some unnecessary whitespace / newlines that needs to be dealt
with, but everything has it’s time, mkay?

This is going to be so much easier to maintain.