Likely, fixing view hierarchy changing during pressHome.

Test RequestPinItemTest.testPinShortcut doesn't wait for the add-to-home
prompt to disappear before proceeding to pressHome. So sometimes
pressHome still sees that prompt that disappears while pressHome is
executing.

Now waiting for the prompt to disappear.

Bug: 155926212
Change-Id: I2c7bfe26839ae406da592e81de8836666c373756