Get absolute path of a python module

This solves several issues related to `RuntimeError: Matching Python module for nupic.xxxxxxx not found`. This is crucial for `pip installable` PR as current errors at Travis are caused by these issues (`pip installable` PR doesn't use `$NTA/lib/python${PYTHON_VERSION}/nupic` longer, but where NuPIC is currently installed on system).

Now we get the path of a python module using the own python interpreter, not more using $NTA. $NTA still is used for get `libcpp_region.so`, but in the future this dynamic library goes to the same place that compiled NuPIC modules, i.e. the system default location for python libraries.