[analyzer][tests] Add normalize_plist to replace diff_plist

Summary:
The `%diff_plist` lit substitution invokes `diff` with a non-portable
`-I` option. The intended effect can be achieved by normalizing the
inputs to `diff` beforehand. Such normalization can be done with
`grep -Ev`, which is also used by other tests.

This patch applies the change (adjusted for review comments) described
in http://lists.llvm.org/pipermail/cfe-dev/2019-April/061904.html to the
specific case shown in the list message. Mechanical changes to the other
affected files will follow in later patches.

Reviewers: NoQ, sfertile, xingxue, jasonliu, daltenty

Reviewed By: NoQ

Subscribers: xazax.hun, baloghadamsoftware, szepet, a.sidorin, mikhail.ramalho, Szelethus, donat.nagy, dkrupp, Charusso, jsji, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D62949

llvm-svn: 362994