python tests bork when more than one system "python" is present

[mylese]

Some systems have Python2 and Python3 installed. When a python module calls "python" it may not get the Python it was expecting. Replacing the call with sys.executable is more explicit.

[Prof Garth Wells]

Fix issue #175: python tests bork when more than one system 'python' is present

→ <<cset 8e2e52a25524>>