setup.py generated by --meta=setup option does not include subpackages when distributions are created

[tedo-benchling]

Describe the bug
Wheel/tar.gz files created by running python setup.py bdist_wheel are missing the nested api/model packages

To Reproduce
Steps to reproduce the behavior:

1. Run openapi-python-client generate --path --meta=setup
2. cd into the generated directory
3. run rm -rf build dist && python setup.py bdist_wheel
4. unzip -l dist/*.whl and note that some of the files are missing

Expected behavior
The generated wheel or tar.gz file should contain all of the files for the package.

OpenAPI Spec File
Any open API json should create this issue.

Desktop (please complete the following information):

• OS: mac os 11.6
• Python Version: 3.6.9
• openapi-python-client version: 0.10.7

Additional context
This was introduced when the "fix" for #520 was merged in #521