Change finishSwigPythonLLDB.py to copy six.py instead of simlink it

Summary: If six.py is simlink'd, an installation won't be able to find it unless it has access to the source tree that lldb was built from.

Reviewers: zturner

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D15422

llvm-svn: 255340