To run the cluster example with cluster monitoring, get the sigar binaries and put them in a dev/sigar directory.
To test the cluster example on a single machine with the existing configuration, run sbt in multiple terminal sessions (or screen session) with at least one instance of RemoteServer on port 2551. For example, you could run:
$ ./sbt project dev run-main geotrellis.dev.RemoteServer 2551
$ ./sbt project dev run-main geotrellis.dev.RemoteServer 2552
and then run a RemoteClient instance on a different port
$ ./sbt project dev run-main run 2553 (select RemoteClient)