R1:7b997359466f

Throw CommandException instead of Exception after `git fetch` failure in repository updates

Summary: Fixes T9966. In this unusual, difficult-to-reach case, we throw `Exception` (which has no censoring) instead of `CommandException` (which has censoring). Throw `CommandException` instead.

Test Plan:
- Hacked up a bunch of stuff in order to hit this: disabled origin validation, origin correction, and pointed repository at a bad domain.
- Verified message is now censored correctly.

{F1022217}…