Create a separate Guice module for OpenPaaS communication

[HoussemNasri]

Description

We should have a separate Guice module for OpenPaaS communication to be able to inject custom RabbitMQ configuration that is specific to OpenPaas.

[chibenwa]

Depends on: #1215

Not really. IMO the too tasks are independant.

We can also write a OpenPaaSAmqpForwardAttribute mailet that is exactly AmqpForwardAttribute but configured using OpenPaaS configuration.

[chibenwa]

Let's create an openpaas.properties file:

# If ommitted default to the channelPool defined by RabbitMQ.properties
rabbitmq.url=amqp(s)://(user:password)@rabbit01:5843/theVhost(,amqp(s)://rabbit02:5843)
# Take the user, password, ssl setting and vhost for the first URL

contact.exchange.name=contact:added

openpaas.admin.username=...
openpaas.admin.password=...

So we create a RabbitMQChannelPool annotated with @Named("openpaas") from the above config and we fallback for the distributed tmail backend to the standard RabbitMQChannelPool.

[chibenwa]

We decided with Houssem to not implement fallback for distributed-app to the main RabbitMQChannelPool.

We can live with 2 pools (we already live with 4 of them!)