[Android] Match overflow menu button

#294

Appium loops forever when searching for multiple buttons if `sel.instance` is used.

`find_elements :tag_name, :button`

```
info: [ANDROID] [info] com.android.uiautomator.core.UiObject@b5060048
info: [ANDROID] [info] keep searching A 1572
info: [ANDROID] [info] com.android.uiautomator.core.UiObject@b4fa0670
info: [ANDROID] [info] keep searching A 1573
```

`adb logcat` shows it's finding the same button over and over again.