revamp app compat test harness

- migrate away from deprecated JUnit3 paradigm
- scan dropbox entries for app errors, instead of probing
  task list
- use IActivityController to suppress crash dialogs and record
  detected app errors
- use combined dropbox and activity controller detected errors
  to determine app errors

Bug: 67002148
Test: run harness against apps known to crash
Change-Id: If108cfdc7474a13e24f0d8350a7cbf99e3b51c46