Fix status icon reappearing for legacy activities

When closing the shade, and underneath was an activity without
colored status bars, the animation for letting the status icons
reappear was strange and the icons faded from 0% alpha. The cause was
possibly that we set hasOverlappingRendering on the whole group but
but inner views used layers for setting the alpha value which
violated the contract in the documentation of
hasOverlappingRendering: "The current implementation of the saveLayer
and saveLayerAlpha methods in Canvas necessitates that a View return
true if it uses the methods internally without passing the
CLIP_TO_LAYER_SAVE_FLAG."

Change-Id: I4b0accc8ec3fb8cb553c6860eb7dba8a12d04364