Various fixes/cleanup in Scenes and Transitions

setDuration() wasn't handled correctly for TransitionGroup; it should
propagate the value to its children.

Also, videos with no ids were not being handled correctly. The transition code was
using the default id on those views (-1) to store start/end data about the view,
causing multiple non-id views to clobber values in the hashmaps. The correct approach
should be to ignore default id values - only store information about the view
instances, not about the unset ids.

Also, added a new test InterruptTest to be used to fix the current behavior of
not handling situations where new transitions start while old ones are still taking place.

Change-Id: I4e880bdbb33cc26d487bceb0d56e463e72f7621f