implement `create_image()` or an `ex_` equivalent in the AzureNodeDriver in azure_arm

I think this must just be something no one's gotten around to yet.

Do you have any guidance on how big an effort it would be to implement this? Are there any known gotchas around Azure that are making this difficult to do?

Start by reviewing the AzureNodeDriver and the existing image-management methods in the azure_arm provider. Determine Azure's requirements and gotchas for creating an image, then define whether create_image() or an ex_ equivalent is appropriate; done means the selected API is implemented and its behavior is covered by the project's relevant tests.

Written by the indexing model from the issue text.