TNL-328 Cohort/server display auto

[TNL-180](https://openedx.atlassian.net/browse/TNL-180)

Note to reviewers: I removed these internal test helper methods since Lines 41-42 came up in the code-coverage report as not ever being used.  I had initially moved the `get_cohort_in_course` helper method into this file in my previous PR, assuming it added value (since it previously existed).  However, there is already a `get_cohort_by_name` method in cohorts.py that is sufficient.