Disabled tests that are failing in Jenkins

This PR temporarily disables acceptance tests in the CMS suite that were failing intermittently on Jenkins.

The disabled tests are:

problem-editor.feature
section.feature (add a new section to a course)
subsection.feature (delete a subsection)

Jenkins has had two clean builds with this branch.  Once we get the test suite running again, we will circle back to fix and re-enable the tests.

Reviewer: @jzoldak