feature: adding basic auth support to kafka contrib apps

This addresses the request for username/password authentication to
certain kafka contrib apps (e.g. http producers). Note that this
requires nginx, and in fact it is designed to run after the default
nginx recipe.

Summary of changes:

1. added contrib_basic_auth.rb recipe
  a. creates and populates a htpasswd-type username/password file
  b. generates an nginx conf file specifying the kafka-contrib app as
     the target of the nginx reverse proxy

2. added kafka_contrib_proxy.conf.erb

3. added two default kafka contrib attributes for generation of the nginx
   conf file from the above template

Squashed commit of the following:

commit 82f0ec7a4cf2d7437b13c3f7636354057cf9af10
Author: Eric Katerman <eric@infochimps.com>
Date:   Tue Jan 21 15:19:28 2014 -0800

    adding basic auth support for kafka contrib apps

    Change-Id: I25e8d041a81a33d3118618078667883d78d1ce7b

Change-Id: I46b08a7b944c4274d8e03252d0d8a82a5d2e4c7d
Merge branch 'master' into gerrit_master

and bumping kafka to 0.5.12

Conflicts:
	cookbooks/kafka/VERSION