Make sure the SSH key we copy to EC2 has permissions 600.

SPARK-539 #resolve

ec2/spark_ec2.py

@@ -361,6 +361,7 @@ def setup_cluster(conn, master_nodes, slave_nodes, zoo_nodes, opts, deploy_ssh_k
     print "Copying SSH key %s to master..." % opts.identity_file
     ssh(master, opts, 'mkdir -p ~/.ssh')
     scp(master, opts, opts.identity_file, '~/.ssh/id_rsa')
+    ssh(master, opts, 'chmod 600 ~/.ssh/id_rsa')
   print "Running setup on master..."
   if opts.cluster_type == "mesos":
     setup_mesos_cluster(master, opts)