Clean up coding style, use vtkNew instead of VTK_CREATE

Cleaned up the coding style used in the testing classes to be more
consistent, removed VTK_CREATE and replaced with vtkNew. Use the
std::string comparisons instead of strcmp.

Change-Id: Id6609b5072a632e1dc65fa5618872add5c38546b
If the original file is missing, make it non-fatal

The external data code makes it hard to add a new test as the test
is used to generate the baseline. Make the missing original a status
message rather than a fatal error. This allows you to add a new test,
compile it, generate the baseline and then add it as we did before the
move the external data.

Change-Id: I7cf25270c59ec1055c9e4c37d9e328f9f696f236
Merge topic 'render-test' into master

32e48028 If the original file is missing, make it non-fatal
592643f7 Clean up coding style, use vtkNew instead of VTK_CREATE