Fix jank when clicking on HUN

There is jank at the beginning of the transition when the heads-up
disappears when clicking, because a lot of stuff is going on. In
order to make it consistent with other notification clicks in the
shade, introduce a delay for the disappear animation.

Bug: 23365512
Change-Id: Ib7c5db552d6803f96374198c2af38cf8236769cd