Added SparkGCE Script for Version 0.9.1

I have added the SparkGCE script in this pull request. Just like the spark_ec2 script, this one also reads certain command-line arguments (See the README.md for more details) like the cluster name and all, then starts the machines in the google cloud, sets up the network, adds a 500GB empty disk to all machines, generate the ssh keys on master and transfer it to all slaves and install java and downloads and configures Spark-v0.9.1/Shark-v0.9.1/Hadoop-v0.9.1. Also it starts the shark server automatically. Currently the version is 0.9.1 but I'm happy to add/support more versions