tests leak vtk objects

[danlipsa]

If we enable VTK_DEBUG_LEAKS the following uvcdat tests fail because they leak VTK objects.

 78 - test_vcs_interact_no_plot (Failed)
105 - test_vcs_taylor_2quads (Failed)
361 - test_vcs_isoline_labels_multi_label_input_types (Failed)
362 - test_vcs_isoline_labels (Failed)
363 - test_vcs_isoline_labelskipdistance (Failed)
364 - test_vcs_isofill_isoline_labels (Failed)
365 - test_vcs_isoline_width_stipple (Failed)
366 - test_vcs_isoline_labels_background (Failed)
419 - test_vcs_animate_isoline_text_labels (Failed)
420 - test_vcs_animate_isoline_text_labels_colored (Failed)
434 - test_vcs_click_info_boxfill (Failed)
435 - test_vcs_click_info_mollweide_boxfill (Failed)
436 - test_vcs_click_info_meshfill (Failed)
437 - test_vcs_click_info_robinson_meshfill (Failed)
438 - test_vcs_click_info_isofill (Failed)
439 - test_vcs_click_info_isoline (Failed)
440 - test_vcs_click_info_vector (Failed)

We should have a buildbot machine that enables this variable.

Might be related to
#1397