Test/development portability

[cnweaver]

This patch collects changes I needed to make to run the tests locally when developing.

Description

This includes:

• Adding a set of optional development dependencies (pytest, etc.)
• Fixing docker image names so that pulls from dockerhub succeed
• Fixing test failures from calling os.path.join on mock objects

Motivation and Context

Without these changes, I could not run the tests in a clean venv (because testing packages are not installed by default), and when i installed these I got large numbers of test failures.

How Has This Been Tested?

After making these changes, and using the new pip install .[dev] option all tests run and pass.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[BrianJKoopman]

Thanks for the PR!

Before merging I'd like to especially clear up the issue I brought up with the changes in the docker-compose file, which might just be a lack of documentation on my part.