Fix flaky test `tests/test_iotedgedev_solution.py::test_push_modules_to_local_registry`

- 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

This test fails from time to time when trying to push to the local registry:

```ERROR: Get "[http://localhost:5000/v2/"](http://localhost:5000/v2/%22): read tcp [::1]:37004->[::1]:5000: read: connection reset by peer.```

See [pipeline run](https://dev.azure.com/Azure-IoT-DDE-EdgeExperience/IoTEdgeDev/_build/results?buildId=3660&view=logs&j=7a9ce834-6c19-5d42-50a9-8919652b4fef&t=58f3d9b9-c9a0-5aed-3a48-2eea66cc08d9).


Steps to Reproduce:

1. Run the corresponding test.