Simple java consumer

Creates a simple blocking java consumer.  It is expected that this code is executed inside of a thread (or something similar)


```ruby
# $bundle exec jruby hermann_test.rb


require 'hermann'
require 'hermann/provider/java_simple_consumer'
require 'hermann_jars'

zookeeper = "localhost:2181"
groupId   = "group1"
topic     = 'test'

example = Hermann::Provider::JavaSimpleConsumer.new(zookeeper, groupId, topic)

example.get_messages do |msg|
  puts "Recv: #{msg}"
end
```

Testing that the `'#to_s` representation of whatever is coming out of the Java layer seems very brittle to me, is this the only way that this can be tested properly?