Add ftrace to detect and end on SIGCHLD

Call ftrace and have it end upon getting a SIGCHLD so we can see what
went on leading up to that time.

Change-Id: I84edb1b470dbadf231ba87e3a5d083fd7088cfa9
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/starter/starterd_lib.h b/aos/starter/starterd_lib.h
index 3779c84..1ffc782 100644
--- a/aos/starter/starterd_lib.h
+++ b/aos/starter/starterd_lib.h
@@ -77,6 +77,8 @@
   aos::PhasedLoopHandler *status_timer_;
   aos::TimerHandler *cleanup_timer_;
 
+  aos::Ftrace ftrace_;
+
   int status_count_ = 0;
   const int max_status_count_;