Fix license file path in Python API CMake file

The CMake file for the Python API, currently fails to copy the license
file to the build directory because it incorrectly assumes that the file
is in the Python API folder.

The license file that should be used is in the top of the repository and
the CMake file has been updated accordingly.

Change-Id: Ia0131cc27abdf28d355c69a556229691901971e5