Fixed problems with psychometrics (Opaque Keys)

@carsongee Some simple fixes to get psychometrics working again:
- Update key comparisons for Opaque Keys
- Search for 'problem_check' instead of 'save_problem_check' when
  filtering TrackingLogs.
Yep. :) https://github.com/mitocw/edx-platform/commit/cd746bf8e5127c6049950ef002c5ca9e1aebed65