Lookup Kafka brokers from Zookeeper

Create a new ```Herman::Providers::JavaProducer``` object with the zookeeper info instead of broker ids.

This removes the functionality of instantiating the JavaProducer object with broker ids.
Based on some IRL conversation, here's what I think we should refactor to:

```ruby
def connect(timeout=0)
  brokers = []
  ZK.open(keepers) do |z|
    brokers = fetch_brokers(z)
  end
  if brokers.empty?
    raise SomeError
  end

  # do connection with a broker list
  connect(brokers.join(','))
end

private
def fetch_brokers(zk)
  brokers = []
  zk.children do |id|
    node = fetch_znode("#{BROKERS_PATH}/#{id}")
    next if node.nil? # whatever error could happen from ZK#get
    brokers << format_broker_from_znode(node)
  end
  return brokers
end

def fetch_znode
end

def format_broker_from_znode
end
```