Some updates for Speed 6/VAR_BASED_PARTITION.

Reduce the intra_cost_penalty for non-rd mode,
and some updates to VAR_BASED_PARTITION.

Visual tests show some improvement at Speed 6, for RTC clips.

Change-Id: If9090daf7aed14906a32d931a538ab544bbca606
Merge "Some updates for Speed 6/VAR_BASED_PARTITION."