Init the current context as NATIVE_APP for Selendroid.

lib/devices/android/selendroid.js

@@ -65,6 +65,7 @@ Selendroid.prototype.init = function () {
     , ['GET', new RegExp('^/wd/hub/session/[^/]+/context')]
     , ['GET', new RegExp('^/wd/hub/session/[^/]+/contexts')]
   ];
+  this.curContext = this.defaultContext();
 };
 
 _.extend(Selendroid.prototype, androidCommon);