Simplify re-running build

[rcj4747]

Write the commands below # Perform the build in generate_build_config.py as a write_files: user-data stanza and then call the shell script on boot. Pulling those commands out of user-data to a script will allow the user to ssh to the instance and easily re-run the build w/o tearing down the instance and re-deploying which could be slow. Alternatively the user would need to view /var/lib/cloud/instance/user-data.txt to find the commands to re-run the build.