Remove returning err and add comment

[arukuka]

Summary

In GetComputationResult, MC behavior was changed to not return an error when MC2CC communication was failed.

Purpose

• If CC container was down, client could not know CC error
  • This patch fixes this
• Related Write error status when CC exited with code non-zero #84

Contents

• 495de01

Testing Methods Performed

• Run demo
  • check that execute_demo.py and progress_demo.py work
  • check behavior when CC container was down

[arukuka]

Re-checked after rebase