Version the bootstrap.sh script we use to pull RPMs to EMR clusters

[CloudNiner]

It's currently available at s3://geotrellis-build-artifacts/rpms/bootstrap.sh but we don't keep it checked in anywhere or version it. We should put it here in this repo and have a process to publish it to the S3 bucket where it currently lives.

[jpolchlo]

The version on S3 looks suspiciously like https://github.com/geotrellis/geotrellis-deployments/blob/master/emr/bootstrap.sh