Modernize Python scripts

Use type destructuring instead of explicit indexing.
This is preparatory work for python2/3 compatibility.

Differential Revision: https://reviews.llvm.org/D55989

git-svn-id: https://llvm.org/svn/llvm-project/test-suite/trunk@350381 91177308-0d34-0410-b5e6-96231b3b80d8