You can now pass an argument to the vtk.web.server that specifies a
Python script to run which can test the server.  The test script will
be run in a separate thread, and can send results back to the main
thread which will signal passage or failure of the test to the ctest
testing framework.

Adding a Python testing module to allow testing of vtk and pv web.

This module allows us to specify an extra command-line argument to
server.py which is a python test script.  The test script will be
run in a separate thread and can communicate it's results back to
the main thread.  All current and future ParaViewWeb applications
automatically have this testing capability.  Test scripts are now
specified as a separate python script in an argument to server.py.

This module also contains several convenience methods which can be
used by any test script.  Useful functions include methods for
indicating whether the test passed or failed, image comparison
methods, etc.

Change-Id: Ia0ada2c56540de9540524975d9865680e4cca5e2