Add the check name to the clang-tidy diagnostic output.

Summary:
Pass check names all the way from ClangTidyModule through
ClangTidyCheck and ClangTidyContext to ClangTidyError, and output it in
handleErrors. This allows to find mis-behaving check and disable it easily.

Reviewers: djasper, klimek

Reviewed By: djasper

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2534

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@199094 91177308-0d34-0410-b5e6-96231b3b80d8