Add AMQPExchange and support AMQPQueue binding to an exchange

[joao-conde]

Issue: https://github.com/ripe-tech/ripe-compose/issues/68

This PR:

• adds an AMQPExchange class that abstracts a connection to a RabbitMQ exchange
• an exchange belongs to a cluster, not a single node; hence, this class accepts a list of broker URLs; if the connection to one fails, it attempts to connect to the rest; if all brokers fail, this class will attempt to reconnect forever (but such a catastrophic failure will likely require a cluster reset regardless)
• changes AMQPQueue class to accept an optional exchange name and routing key; if present, it binds the queue to that exchange using that routing key

[coveralls]

Coverage decreased (-0.1%) to 63.718% when pulling de9f12b on joao-conde:master into ad27856 on hivesolutions:master.

[coveralls]

Coverage decreased (-0.1%) to 63.727% when pulling 606f7eb on joao-conde:master into ad27856 on hivesolutions:master.

[joao-conde]

Forgot to tag back then @joamag

[joao-conde]

@joamag probably worth to reaper this