Simplify orchestration adapter client

@alexwelch Decided to go ahead and strip this down to just the basic code we need for this client. I'm still using Faraday so it's similar to our other clients, just without all the ceremony.

Also, added specs.
Yeah? You think I should just fold everything right into this file? I don't know why I resisted that initially -- I guess I was holding on to the idea that this thing might grow and there'd be some other logic we'd want here at the module level but not in the client itself.  Probably a YAGNI scenario though.