Sagemaker-mxnet-training

Bug fixes and other changes

* split cpu and gpu test commands.

Bug fixes and other changes

* add flake8 in buildspec.yml and fix flake8.
* fix placeholder name cpu-instance-type in buildspec-release.yml
* Add eu-west-3, eu-north-1, sa-east-1 and ap-east-1 to the no-p2 regions.

Features

* add MXNet 1.4.1 Dockerfiles

Bug fixes and other changes

* fix build directory in scripts/build_all.py
* fix copy command in buildspec-release.yml

Bug fixes and other changes

* remove JSON syntax error from buildspec-release.yml

Bug fixes and other changes

* Updating SageMaker Containers to the latest version

Bug fixes and other changes

* pin sagemaker in test dependencies