load 'observer' application and fix issue #557

rel/reltool.config

@@ -20,6 +20,7 @@
          goldrush,
          compiler,
          runtime_tools,
+         {observer, load},
          lager,
          gen_logger,
          gproc,
@@ -56,6 +57,7 @@
        {app, inets, [{incl_cond, include}]},
        {app, compiler, [{incl_cond, include}]},
        {app, runtime_tools, [{incl_cond, include}]},
+       {app, observer, [{incl_cond, include}]},
        {app, goldrush, [{incl_cond, include}]},
        {app, gen_logger, [{incl_cond, include}]},
        {app, lager, [{incl_cond, include}]},