take II: variance_test partial clean-up
take II: variance_test partial clean-up

remove some (but not all yet!) tuple mis-use, and revamp the code a lot.
Factorize some common chores into MainTestClass.

Change-Id: Id37b7330eebe80d19b9d12a454f24ff9be6b1116

smarter/aom,smarter/aom,GrokImageCompression/aom,luctrudeau/aom,mbebenita/aom,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,luctrudeau/aom,luctrudeau/aom,smarter/aom,luctrudeau/aom,smarter/aom,smarter/aom,mbebenita/aom,GrokImageCompression/aom,GrokImageCompression/aom,smarter/aom,GrokImageCompression/aom,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom