Run connection.start each time we access RabbitMQ connection
Run connection.start each time we access RabbitMQ connection

We regularly see an error of `undefined method `next_channel_id' for
nil:NilClass` which seems to be when bunny has dropped it's connection
or doesn't have one.

Running connection.start each time we'll restore one if it's gone and
not cause a problem if one already exists:
https://github.com/ruby-amqp/bunny/blob/master/lib/bunny/session.rb#L286-L287

alphagov/publishing-api,alphagov/publishing-api