AURORA-88: get_quota -h lists --cluster as deprecated

Replaces CLUSTER_INVOKE_OPTION with a new CLUSTER_NAME_OPTION so that
get_quota -h shows the correct help dialog.

Reviewed at https://reviews.apache.org/r/17637/
AURORA-193: License header cleanup

Adds license header checks and the gradle license header plugin.

Bugs closed: AURORA-193

Review: https://reviews.apache.org/r/17717/