We currently support skipping unified spec tests by name.  However, the current implementation doesn't support adding a skip reason to the skipped tests, so no justification for the skip is printed in the test output.  We should enhance our runner to allow specifying the skip reason, so that skip reasons are included in the test output.

Acceptance Criteria

• enhance the unified test helpers to take a skip reason in addition to an array of tests to skip
• audit existing usages of `runUnifiedSuite` and add skip reasons to any existing skipped tests (where applicable)