Use new ChefSpec.start! method for coverage reporting
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.
Use `dotted` notation for configuration attributes as well

This commit makes it possible to use either underscored symbol keys for
configuration attributes (i.e. attributes defined under `broker`), or to
use the `dotted` notation, i.e.

```
node.set.broker.log_dirs = %w[/some/dir-1 /some/dir-2]
node.set.broker.log.dirs = %w[/some/dir-1 /some/dir-2]
node.set.broker = {‘log.dirs’ => %w[/some/dir-1 /some/dir-2]}
```

Are all valid ways to set attributes that will be used when rendering
the broker configuration file. Got rid of quite a lot of unit tests that
simply aren’t needed anymore, yay.