Run karma-ci script from karma rake task and set karma-ci to use log-level flag set to debug

What does this MR do?

I was struggling a lot with a karma job that was failing on CI, but didn't have any errors at all. Somehow, using --log-level debug revealed the errors.

Before:

https://gitlab.com/gitlab-org/gitlab-ce/builds/16216019

After:

https://gitlab.com/gitlab-org/gitlab-ce/builds/16229768

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?