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}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9966

Differential Revision: https://secure.phabricator.com/D14745

src/applications/repository/engine/PhabricatorRepositoryPullEngine.php

@@ -334,12 +334,12 @@ final class PhabricatorRepositoryPullEngine
             $remote_uri);
         }
       } else if ($err) {
-        throw new Exception(
-          pht(
-            "git fetch failed with error #%d:\nstdout:%s\n\nstderr:%s\n",
-            $err,
-            $stdout,
-            $stderr));
+        throw new CommandException(
+          pht('Failed to fetch changes!'),
+          $future->getCommand(),
+          $err,
+          $stdout,
+          $stderr);
       } else {
         $retry = false;
       }