rtemstoolkit: Add unit testing for the python modules

- Add support to run the unit tests for the rtemstoolkit python
  modules from waf. Enter './waf test' for the tests to be run on
  python2 and python3.
- Update the importing of rtemstoolkit modules to the standard
  method which works on python2 and python3.
- Update the README.

rtemstoolkit/rtems.py

@@ -71,7 +71,10 @@ def configuration_path(prog = None):
      2. Ok to directly call os.path.
     '''
     if prog is None:
-        exec_name = sys.argv[1]
+        if len(sys.argv) == 1:
+            exec_name = sys.argv[0]
+        else:
+            exec_name = sys.argv[1]
     else:
         exec_name = prog
     exec_name = os.path.abspath(exec_name)