add packageAndLaunchActivity support for selendroid

also convert our tests to use this by default so that it's tested
also move it to after prepareDevice so we make sure to run adb commands
with the appropriate device id etc
fix #2083, cc @bootstraponline

test/functional/android/apidemos/desired.js

@@ -4,7 +4,5 @@ var getAppPath = require('../../../helpers/app').getAppPath;
 
 module.exports = {
   app: getAppPath('ApiDemos', 'android'),
-  device: 'Android',
-  'app-package': 'com.example.android.apis',
-  'app-activity': '.ApiDemos'
+  device: 'Android'
 };