[LoopInterchange] Update tests so DA can handle access after D35430.

I have taken the opportunity to simplify some tests slightly and move
parts around.

It also brings back a few IR checks for interchangable loops.

Reviewers: karthikthecool, sebpop, grosser

Reviewed By: sebpop

Differential Revision: https://reviews.llvm.org/D45207

llvm-svn: 329081