Fix flaky tests tests/test_iotedgedev_solution.py

[beandrad]

• iotedgedev Version: v3.3.4
• Python Version: 3.6
• Pip Version:
• Development machine OS Version: Ubuntu 20.04
• IoT Edge device OS Version: Ubuntu 20.04

The tests that call create_solution() in tests/test_iotedgedev_solution.py fail when the directory where the edge solution needs to be created is not empty. This happens when the files from a previous pipeline run are still there. The directory should be clean up on test setup and teardown.

Exception: ERROR: Directory is not empty. Run `iotedgedev iothub setup` to retrieve or create required Azure resources or clean the directory.

See pipeline run.

Steps to Reproduce:

1. Run the corresponding tests in tests/test_iotedgedev_solution.py