Disable known hosts when SSH'ing through Drydock

Summary: This prevents SSH from saving the host key into known_hosts; StrictHostKeyChecking only prevents it from prompting for unknown hosts, but it will still verify hosts against what it has previously saved.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10252

src/applications/drydock/interface/command/DrydockSSHCommandInterface.php

@@ -86,6 +86,7 @@ EOF;
     return new ExecFuture(
       'ssh '.
       '-o StrictHostKeyChecking=no '.
+      '-o UserKnownHostsFile=/dev/null '.
       '-o BatchMode=yes '.
       '%C -p %s -i %P %P@%s -- %s',
       $command_timeout,