Defer paravieweb testing dependency checks until runtime
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
Currently the configure process is checking for the presence of python modules, as well as checking for selenium webdrivers to be installed before scheduling tests. In the case of Firefox, this has resulted in having to actually pop up a browser window (several times) during the configure process, which has been frustrating and slowed down the process.
This change takes advantage of a recent change in VTK Web where all testing dependency checks can now be done at runtime. Currently, tests that don't meet dependency requirements are simply allowed to pass. However, as soon as ParaView depends on CMake 3.0, we can start taking advantage of a new CMake feature ("SKIP_RETURN_CODE"), which will allows tests to return a special value that will indicate to CTest that the test was not run because dependencies were not met.