Fix image comparison test

Make the comparison test use clean vistrails preferences file like
the other tests were made to do in improve_build branch.
Tests can not use the users vistrails preference file since that tends
to get out of synch. In that case we get messages about missing
fundamental vistrails packages (spreadsheetcell).
add logo to regression test images
forgot to add logo to interactive test image
Remove dependency of image validation on VTK

We can't depend on VTK for testing since ParaView (and thus VTK)
are optional. So this change replaces the call to vtk's regression
test image infrastructure with a home grown comparison.

The new comparisons no longer require pure RGB images, and work
on any format as long as a suitable matching baseline file can
be found. Therefor the old A stripped baseline images are being
replaced.

However the new tests don't use the trusted metric for image sameness
and use a simple rms comparison instead. The new tests also don't output
enough informaiton for ctest to show the test results images on the dashboard.
add new regression images for ubuntu
Merge remote-tracking branch 'devel/new_test_validation'

* devel/new_test_validation:
  add new regression images for ubuntu
  Remove dependency of image validation on VTK
  forgot to add logo to interactive test image
  add logo to regression test images
  Fix image comparison test