servers.yaml's 'xd: -> transport: rabbit' overrides xd-singlenode's default of local transport

When working w/ SXD xd-singlenode, out of the box, it defaults to using all embedded components (transport, analytics, hsqldb, & zookeeper), which is easy and a great way to get going. This is also great for development.

When I then started trying out the M6 distributed mode I set my transport to rabbit in servers.yaml (now that the --transport option is gone). Rabbit is my preferred transport here.

I then went back to running the singlenode, for simplicity, and then got an exception saying that the singlenode couldn't contact RabbitMQ/AMQP (I was no longer running rabbit). I then had to add the '--transport local' flag back to xd-singlenode.

Having the --transport option on xd-singlenode but not on xd-container is confusing. Also I would expect xd-singlenode to default to local transport unless I specify another option in --transport.

-Derek