BUG: Examples should build if BUILD_TESTING is OFF

With BUILD_EXAMPLES:ON and BUILD_TESTING:OFF, the Examples should
compile.

To configure VTK with BUILD_EXAMPLES:ON and BUILD_TESTING:OFF, from an
empty build tree,

cmake  -DBUILD_TESTING:BOOL=OFF -DCMAKE_BUILD_TYPE:STRING=Release vtk_src_tree

NOTE: If you have already configured VTK with default settings, you
must clean the build tree and rerun cmake with the above
setting. Otherwise, bogus tests will remain.

Conflicts:
	Examples/IO/Cxx/CMakeLists.txt
	Examples/ImageProcessing/Cxx/CMakeLists.txt
	Examples/Medical/Cxx/CMakeLists.txt
	Examples/Modelling/Cxx/CMakeLists.txt
	Examples/VisualizationAlgorithms/Cxx/CMakeLists.txt
	Examples/Widgets/Cxx/CMakeLists.txt

Change-Id: I996065a30aab43cca630a369b39d748de728039b