Timeout on RabbitMQ startup

Prior to this pull request, we've seen issues where starting AppScale on multiple nodes in EC2 would fail because RabbitMQ would fail to start up. As we are not entirely sure why this is happening, a hack for the moment is to not wait forever for RabbitMQ to start. Future work is looking into why RabbitMQ isn't starting up correctly.

As this branch has (https://github.com/AppScale/appscale/pull/305) merged into it, don't pull this in until that branch gets merged.