WIP: Redis sentinel support. Depends on #65

These changes add a new LWRP and recipe to configure a sentinel. You must first use the install LWRP or recipe to install redis onto the node then use the sentinel LWRP/recipe to configure and create an init script. 

Currently does not include an upstart style init script. 

Configure sentinel the same way as a redis server:

    'sentinels' => [
      {'name' => 'mymaster'},
    ]