docs(gce): instructions for running Deis in Google Compute Engine

Adding instructions and script for running on Google Compute Engine. This changes existing CoreOS user-data to set permissions as strings instead of integers. PyYAML interperets integers preceded by 0 to be octal. 0755 would become 493 when converted.

closes #1036
Merge pull request #1495 from andyshinn/google_compute_engine_tutorial

docs(gce): Instructions for running Deis in Google Compute Engine