Refactor test_intra_pred_speed.
Refactor test_intra_pred_speed.

This will make it easier to add the rest of the transform sizes (larger
than 32x32 blocks and 1:4 rectangular blocks).

BUG=aomedia:1307

Change-Id: I7364ba82432436fa3f7379d17a2d283cca5a5d2a

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom