
This PS enforces the design requirement that says that only 1 layering policy can exist in the system at once. Attempting to create another layering policy with a different name is a 409 error. The existing layering policy can be updated by passing in a document with the same `metadata.name` and `schema` as the existing one. Closes-Bug: https://github.com/att-comdev/deckhand/issues/12 Change-Id: I7cad2d600c931c8701c3faaf2967be782984528b