Update TESTING.md
Update TESTING.md

Updated instructions for running unit tests under Python 2.7.
ddebrunner/streamsx.topology,IBMStreams/streamsx.topology,IBMStreams/streamsx.topology,IBMStreams/streamsx.topology,ddebrunner/streamsx.topology,ddebrunner/streamsx.topology,IBMStreams/streamsx.topology,ddebrunner/streamsx.topology,IBMStreams/streamsx.topology,ddebrunner/streamsx.topology,IBMStreams/streamsx.topology,ddebrunner/streamsx.topology,IBMStreams/streamsx.topology,ddebrunner/streamsx.topology