Implement reconnect logic for AMQP EventReader

Implemented functionality that handles reconnecting to the amqp server
and reinitializing the amqp channel in case of errors and timeouts. This
is handled by a goroutine created in the client constructor (it also
handles the initial connect/init).

Reconnects and reinits will use a fibonacci backoff strategy, and the
attempt amount and max waiting interval can be adjusted by the
'reconnects' and 'max_reconnect_interval' config options.

Messages that fail processing are now dropped instead of being requeued,
preventing infinite processing loops. However, this means that the
messages are lost. Handling failed messages will need to be addressed
separately.

'concurrent_requests' will now set the prefetch count. Setting the
prefetch count using the Qos function was able to replace our old
approach that was using channels. Default value is 1024 which,
according to the rabbitmq docs, 'runs into the law of diminishing
returns'. The recommended value is between 100-300. Source:
https://www.rabbitmq.com/confirms.html#channel-qos-prefetch-throughput

Fix test compilation errors caused by these changes.

References cgrates#4160