COMP: Block tests when VTK_USE_CG_SHADERS Off

Some tests require VTK_USE_CG_SHADERS On. Block them if off.

Change-Id: Ifa11bc69fcde319af88a0100c2c7274f6265487b
Merge topic 'CgShadersGuard' into master

8e906f1e COMP: Block tests when VTK_USE_CG_SHADERS Off