Resolve Sonar Security Issues

[ArBridgeman]

Summary

There are many different issues, so I'd tackle them in multiple PRs.

• https://sonarcloud.io/component_measures?id=com.exasol%3Apython-toolbox&metric=security_rating&view=list

• For the small ones, see if you can also fix:

https://sonarcloud.io/project/issues?impactSoftwareQualities=MAINTAINABILITY&issueStatuses=OPEN%2CCONFIRMED&id=com.exasol%3Apython-toolbox