[lit, python3] Update lit error logging to work correctly in python3 and other test fixes

Summary:
In Python2 'unicode' is a distinct type from 'str', but in Python3 'unicode' does not exist and instead all 'str' objects are Unicode string. This change updates the logic in the test logging for lit to correctly process each of the types, and more importantly, to not just fail in Python3.

This change also reverses the use of quotes in several of the cfg files. By using '""' we are guaranteeing that the resulting path will work correctly on Windows while "''" only works correctly sometimes. This also fixes one of the failing tests.

Reviewers: asmith, zturner

Subscribers: stella.stamenova, delcypher, llvm-commits

Differential Revision: https://reviews.llvm.org/D50397

llvm-svn: 339179