We heavily utilize Akka clustering for our backend and we do this using Akka's multi-node testing feature.

http://doc.akka.io/docs/akka/2.2.1/dev/multi-node-testing.ht...

For the most part we only spin up multiple JVMs on the same machine but it's not a huge leap to use multiple machines. We don't do so regularly because, as you said, Vagrant takes forever to spin up a new VM. Our Jenkins server does spin up multiple JVMs for our integration tests though.