Release 68 Turquoise Jay

Small release to handle changes to the AWS Elastic MapReduce APIs.

• Blog post

EmrEtlRunner

• Bumped to 0.16.0
• Bumped Elasticity to 6.0.2 (#1903)
• Named the processing bucket in its associated "is not empty" error (#1911)
• Made in bucket an array (#1750)
• Determined path to Hadoop enrich based on its version (#1789)
• Added unit test for add_trailing_slashes function (#1904)