Adding support for creating and deleting affinity groups

This pull request adds support for creating and deleting affinity groups using the CLI. It has a dependency on another pull request in the SDK project: https://github.com/WindowsAzure/azure-sdk-for-node/pull/569

This is a replacement for PR https://github.com/WindowsAzure/azure-sdk-tools-xplat/pull/174 and is now complete with unit tests and based on the dev branch.