Do not show PipMenuActivity during expansion

When PiP window is enlarged to its expanded state, show the menu after
the expand transition is completed.

Video: http://go/recall/-/aaaaaabFQoRHlzixHdtY/PEn28BT2vdPmCMU6Cqpqy
Bug: 150810705
Test: manual
Change-Id: I62fd28e5568865de12d868719de401aabeb78d13