* First failing test, and enough framework to run it.
* Rudimentary passing test.
* Sagemaker Notebook Support, take-1: create, describe, start, stop, delete.
* Added list_tags.
* Merged in model support from https://github.com/porthunt/moto/tree/sagemaker-support.
* Re-org'd
* Fixed up describe_model exception when no matching model.
* Segregated tests by Sagemaker entity. Model arn check by regex..
* Python2 compabitility changes.
* Added sagemaker to list of known backends. Corrected urls.
* Added sagemaker special case to moto.server.infer_service_region_host due to irregular url format (use of 'api' subdomain) to support server mode.
* Changes for PR 3105 comments of July 10, 2020
* PR3105 July 10, 2020, 8:55 AM EDT comment: dropped unnecessary re-addition of arn when formulating model list response.
* PR 3105 July 15, 2020 9:10 AM EDT Comment: clean-up SageMakerModelBackend.describe_models logic for finding the model in the dict.
* Optimized imports
Co-authored-by: Joseph Weitekamp <jweite@amazon.com>
