Improve starter_cmd status output

This makes "starter_cmd status" output the time since an application
was started. If you specify an application, it outputs
the application name, time since last started, and state.

Change-Id: Ibccaa19f12c8e7c4cdde384f9594ab7c00ae5224
diff --git a/aos/starter/starter_rpc_lib.h b/aos/starter/starter_rpc_lib.h
index 152016a..24c757e 100644
--- a/aos/starter/starter_rpc_lib.h
+++ b/aos/starter/starter_rpc_lib.h
@@ -2,6 +2,7 @@
 #define AOS_STARTER_STARTER_RPC_LIB_H_
 
 #include <chrono>
+#include <optional>
 
 #include "aos/configuration.h"
 #include "aos/starter/starter_generated.h"
@@ -32,7 +33,7 @@
 
 // Fetches the entire status message of starter. Creates a temporary event loop
 // from the provided config for fetching.
-const aos::FlatbufferVector<aos::starter::Status> GetStarterStatus(
+std::optional<const aos::FlatbufferVector<aos::starter::Status>> GetStarterStatus(
     const aos::Configuration *config);
 
 }  // namespace starter