Connector plugins require mcollective/exceptions

If an error message is received (instead of a regular message type) by the plugin the thrown exception fails because the exceptions have not been required. Hence the following message is generated

    The ping application failed to run: uninitialized constant MCollective::Connector::Rabbitmq::UnexpectedMessageType

instead of 

    The ping application failed to run: Received frame of type 'ERROR' expected 'MESSAGE'