#162: Make sure that all docker function calls use docker credentials if possible

[tkilias]

All Submissions:

• [x] Is the title of the Pull Request correct?
• [x] Is the title of the corresponding issue correct?
• [x] Have you updated the changelog?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Are you mentioning the issue which this PullRequest fixes ("Fixes...")
• [x] Before you merge don't forget to run all tests for all Exasol version, by adding [run all tests] to the commit message

[tkilias]

As an alternative, we could also use https://docker-py.readthedocs.io/en/stable/client.html#docker.client.DockerClient.login