Pythonize the tests calls

This PR aims:
- Replace `run_tests.sh` to a more cross platform and default approach. I.e. the `run_nupic_tests` executable script.
- Replace all tests calls from `make` to `$NUPIC/scripts/run_nupic_tests` (except `testpyhtm` which is called from `$NUPIC/bin`).

It allows any user to type `$NUPIC/scripts/run_nupic_tests` in everywhere* on shell and to have access to all nupic tests. Example:

`$ $NUPIC/scripts/run_nupic_tests --help`