Major Description
Right now if people want to launch multiple executors on each machine they need to start multiple standalone workers. This is not too difficult, but it means you have extra JVM's sitting around.
We should just allow users to set a number of cores they want per-executor in standalone mode and then allow packing multiple executors on each node. This would make standalone mode more consistent with YARN in the way you request resources.
It's not too big of a change as far as I can see. You'd need to:
1. Introduce a configuration for how many cores you want per executor.
2. Change the scheduling logic in Master.scala to take this into account.
3. Change CoarseGrainedSchedulerBackend to not assume a 1<->1 correspondence between hosts and executors.
And maybe modify a few other places.
