Close app before starting test.

Try closing the app to see if it fixes the test failure. The test failed
because the app was already in desktop mode, so the assertion that it
has the desktop mode initial bounds failed.

Fixes: 396856948
Test: atest EnterDesktopWithDragPortrait
Flag: EXEMPT test fix
Change-Id: I98c299a054f45c0967f05569a8d475de846c877b