[clang-tidy] Return non-zero exit code for clang errors.

Summary:
Updated tests broken by this change.
Fixes https://bugs.llvm.org/show_bug.cgi?id=27628

Reviewers: ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: klimek, xazax.hun, cfe-commits

Differential Revision: https://reviews.llvm.org/D45258

llvm-svn: 329579