Fixes and cleanups for the multinode setting. (#143)

* Add function for driver to get address info from Redis.

* Use Redis address instead of Redis port.

* Configure Redis to run in unprotected mode.

* Add method for starting Ray processes on non-head node.

* Pass in correct node ip address to start_plasma_manager.

* Script for starting Ray processes.

* Handle the case where an object already exists in the store. Maybe this should also compare the object hashes.

* Have driver get info from Redis when start_ray_local=False.

* Fix.

* Script for killing ray processes.

* Catch some errors when the main_loop in a worker throws an exception.

* Allow redirecting stdout and stderr to /dev/null.

* Wrap start_ray.py in a shell script.

* More helpful error messages.

* Fixes.

* Wait for redis server to start up before configuring it.

* Allow seeding of deterministic object ID generation.

* Small change.

scripts/start_ray.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+ROOT_DIR=$(cd "$(dirname "${BASH_SOURCE:-$0}")"; pwd)
+
+python "$ROOT_DIR/start_ray.py" "$@"