kill all (possibly lingering) containers before starting tox run

Author: kristjanvalur

.github/workflows/integration.yaml

@@ -56,6 +56,7 @@ jobs:
          run: |
            pip install -U setuptools wheel
            pip install -r dev_requirements.txt
+           docker rm -f $(docker ps -a -q)
            tox -e ${{matrix.test-type}}-${{matrix.connection-type}}
        - name: Upload codecov coverage
          uses: codecov/codecov-action@v2