android GTS-- com.google.android.xts.placement.UiPlacementTest fail

    Google要求将GooglePlayStore应用配置在defaul home screen，且default home screen只能配置Gooogle Search Widget，PlayStore，Google Colletion Folder具体如下：

The default home screen features the following placements:

1. Google Search Widget

2. Google Collection folder containing the Core GMS app icons

3. Play Store app icon

com.google.android.xts.placement.UiPlacementTest是检测GooglePlayStore在默认主屏配置正确，否则跑GTS时，该项会fail，如下：

com.google.android.xts.placement.UiPlacementTest
-- testPlayStore	fail	java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.test.uiautomator.UiObject2.click()' on a null object reference at com.google.android.xts.placement.UiPlacementTest.tryElement(UiPlacementTest.java:73)

将GooglePlayStore配置在主屏即可pass。