Changes to partition breakout rules.

Changes to partition breakout rules.

Changes to the breakout behavior for partition selection.
The biggest impact is on speed 0 where encode speed in
some cases more than doubles with typically less than 1%
impact on quality.

Speed 0 encode speed impact examples
Animation test clip: +128%
Park Joy:  +59%
Old town Cross: + 109%

Change-Id: I222720657e56cede1b2a5539096f788ffb2df3a1