Executor: Cross-year student ID matching

[johncmerfeld]

Open question: I think it's technically possible for the second pass to not match anything at all. It would probably produce a result set of empty files which we may not want to upload. Do we just skip in that case?

Implement cross-year matching in the executor; companion to #62. The core logic here is

• IF the app says there is a cross-year roster is available
  • AND this is an ODS job
    • AND there are unmatched students from Earthmover
      • THEN run earthmover a second time on those unamtched students, using a roster we pull from EDU as a year-agnostic source of IDs
  • AND this is NOT and ODS
    • THEN perform a single Earthmover pass, using the EDU roster as the source of IDs
• Otherwise behave normally

Other notes:

• Includes fixes from Fix: Executor can fail to send error body #61 and Fix: Executor should not send unmatched students file when Earthmover fails #63
• When it happens, the second EM pass is special in that it
  • switches the input file
  • switches the roster file
  • eliminates the match rate thresholds
• It is not special in that it
  • still returns unmatched students to the user
  • still assumes a potentially hostile file encoding