Stop SshCommandDestroy thread pool on server shutdown

This avoids leaking the thread during acceptance tests.

Change-Id: I18a7f57bc6b381f28006a20b6cffda0be6b3fb46

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshModule.java

@@ -107,6 +107,7 @@ public class SshModule extends FactoryModule {
         listener().toInstance(registerInParentInjectors());
         listener().to(SshLog.class);
         listener().to(SshDaemon.class);
+        listener().to(CommandFactoryProvider.class);
       }
     });
   }