[SPARK-8596] [EC2] Added port for Rstudio

This would otherwise need to be set manually by R users in AWS.

https://issues.apache.org/jira/browse/SPARK-8596

Author: Vincent D. Warmerdam <vincentwarmerdam@gmail.com>
Author: vincent <vincentwarmerdam@gmail.com>

Closes #7068 from koaning/rstudio-port-number and squashes the following commits:

ac8100d [vincent] Update spark_ec2.py
ce6ad88 [Vincent D. Warmerdam] added port number for rstudio

ec2/spark_ec2.py

@@ -505,6 +505,8 @@ def launch_cluster(conn, opts, cluster_name):
         master_group.authorize('tcp', 50070, 50070, authorized_address)
         master_group.authorize('tcp', 60070, 60070, authorized_address)
         master_group.authorize('tcp', 4040, 4045, authorized_address)
+        # Rstudio (GUI for R) needs port 8787 for web access
+        master_group.authorize('tcp', 8787, 8787, authorized_address)
         # HDFS NFS gateway requires 111,2049,4242 for tcp & udp
         master_group.authorize('tcp', 111, 111, authorized_address)
         master_group.authorize('udp', 111, 111, authorized_address)