Added template support for /etc/default/sensu

Only a single variable is managed in /etc/default/sensu, EMBEDDED_RUBY. It is defaulted to false for compatibility reasons, but if you want to set it to true you can now specify use_embedded_ruby => true in the sensu class.

Example:
  class { 'sensu':
     rabbitmq_password  => 'mypass',
     rabbitmq_host      => 'yourhost',
     subscriptions      => [ 'sensu-general',
                             'sensu-ss',
     ],
     install_repo       => false,
     use_embedded_ruby  => true, 
  }