Add the missing test baseline comparisons

[jhlegarreta]

There are a number of tests whose output is not yet being compared to a baseline, e.g. itkFFTPadPositiveIndexImageFilterTest.

The tool could be improved by steadily adding the baseline images to the corresponding folder, and add the --compare-MD5 flag with the appropriate arguments to the corresponding test in the CMakeLists.txt file.

I may be able to help with the task.