Refactor `binary` recipe to use `build` directory as well
Refactor strings and file paths for checking if kafka is installed
Remove `unless` check in {binary,source} recipes

Not really necessary since everything is handled using notifications
and thus it's only the `remote_file` resource that needs a `not_if`
block.
Add helper for creating download uri for Kafka archives
Add `kafka_download` LWRP

Instead of having duplicated logic in both `binary` and `source` recipes
for downloading and validating the downloaded archive, they're now in a
quite simple LWRP.
Remove unused `installed_path` variable from recipes
Add `kafka_install` LWRP

Wraps a simple `execute` resource, but I'd like to think that the
recipes got a bit nicer looking from using it, and there's a little
less duplication (even though not completely removed).
Extract `build_dir` to attribute
Remove leftover `let` variables in unit tests
Rename `kafka_already_installed?` to `kafka_installed?`
Don't remove build_dir after install
Consistent usage of `File` vs. `::File` in recipes
Remove explicit `:create` in `kafka_download` LWRP
Add common boilerplate comments to LWRPs / libraries

Seems to be some kind of convention for cookbooks.
Remove `use_inline_resources` from `kafka_install` provider
Don't validate md5 checksum if not set

But log a debug message instead.
Prefer `%()` syntax over `""`
A few leftover `File` statements
Merge pull request #19 from mthssdrbrg/dry-recipes

Dry'ed up recipes