Expose internal config parameters for starting Ray (#3246)

## What do these changes do?

This PR exposes the CL option for using a config parameter. This is important for certain tests (i.e., FT tests that removing nodes) to run quickly.

Note that this is bad practice and should be replaced with GFLAGS or some equivalent as soon as possible.

#3239 depends on this.

TODO:
 - [x] Add documentation to method arguments before merging.
 - [x] Add test to verify this works?

## Related issue number

python/ray/test/cluster_utils.py

@@ -111,15 +111,17 @@ class Cluster(object):
         assert not node.any_processes_alive(), (
             "There are zombie processes left over after killing.")
 
-    def wait_for_nodes(self, retries=20):
+    def wait_for_nodes(self, retries=30):
         """Waits for all nodes to be registered with global state.
 
+        By default, waits for 3 seconds.
+
         Args:
             retries (int): Number of times to retry checking client table.
         """
         for i in range(retries):
             if not ray.is_initialized() or not self._check_registered_nodes():
-                time.sleep(0.3)
+                time.sleep(0.1)
             else:
                 break