[lit] Avoid deprecated dict.has_key() method.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187917 91177308-0d34-0410-b5e6-96231b3b80d8
[lit] Use list comprehensions instead of map().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187918 91177308-0d34-0410-b5e6-96231b3b80d8
[lit] Avoid comparisons with None.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187919 91177308-0d34-0410-b5e6-96231b3b80d8
[lit] Report the traceback when config import fails.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187920 91177308-0d34-0410-b5e6-96231b3b80d8