Set dockerd default log-level to warning

[madelen-at-work]

Reduce the default log level of dockerd to warn

Checklist before requesting a review

• [X] I have performed a self-review of my own code
• [X] I have verified that the code builds perfectly fine on my local system
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have commented my code, particularly in hard-to-understand areas
• [X] I have verified that my code follows the style already available in the repository
• [ ] I have made corresponding changes to the documentation