Configure the client queue using a block

Using a block provides access to the `name` attribute.
Change instance variable references to block ones
Allow use of heartbeat option to rabbitmq connect

The default value for the heartbeat option is 0, or disabled. Therefore the
functionality of Sensu will remain unchanged by default. We should provide
users the freedom to weigh the advantages and disadvantages of setting this
option.
Merge pull request #451 from bwong114/allow_heartbeat

Allow use of heartbeat option to rabbitmq connect
Merge pull request #452 from bwong114/use_queue_block

Use a block to create the queue