Give all commands from DiffusionCommandEngine a default 15 minute timeout

Summary:
Ref T13108. See PHI364. See the task and issue for discussion.

If a `git fetch` during synchronization hangs, the whole node currently hangs. While the causes of a `git fetch` hang aren't clear, we don't expect synchronization to ever reasonably take more than 15 minutes, so add a default timeout.

Test Plan: Will deploy and observe; this is difficult to reproduce or test directly.

Maniphest Tasks: T13108

Differential Revision: https://secure.phabricator.com/D19235

src/applications/diffusion/protocol/DiffusionCommandEngine.php

@@ -135,6 +135,11 @@ abstract class DiffusionCommandEngine extends Phobject {
 
     $future->setEnv($env);
 
+    // See T13108. By default, don't let any cluster command run indefinitely
+    // to try to avoid cases where `git fetch` hangs for some reason and we're
+    // left sitting with a held lock forever.
+    $future->setTimeout(phutil_units('15 minutes in seconds'));
+
     return $future;
   }