Disable timers on aos::Application on drop

The issue occurs when an application doesn't live for the duration
of the event loop. Originally, we were seeing segmentation faults
due to timer handlers being called after the application had been
dropped. We now do the proper cleanup to avoid this.

Change-Id: I42b474e72a536f9332b757a853edae471f29fc6c
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/starter/subprocess.cc b/aos/starter/subprocess.cc
index 36e780a..f5563e6 100644
--- a/aos/starter/subprocess.cc
+++ b/aos/starter/subprocess.cc
@@ -663,4 +663,12 @@
   }
 }
 
+Application::~Application() {
+  start_timer_->Disable();
+  restart_timer_->Disable();
+  stop_timer_->Disable();
+  pipe_timer_->Disable();
+  child_status_handler_->Disable();
+}
+
 }  // namespace aos::starter