[tests] Reapply r188354, ensure subsitution string is ascii.

 - Now fixed to ensure substitution value isn't of unicode type on Python 2.6-7.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188384 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed