Wrap docker client with a thread pool executor
Comments and bump up
Send async_docker_client to the culler
Wrap exception handling around the culler.
Make dock workers configurable, check callable.
Configure an executor rather than number of workers
Fix up options, comments
Merge pull request #39 from rgbkrk/docker_async

Wrap docker client with a thread pool executor
Split out Docker pieces and rename to orchestrate.

* dockworker & orchestrate are the main drivers
* Relies on default docker settings
* gitignore python remnants
* Wrap killing and removing a container