BUG: Make ITKTestKernel a test dependency
BUG: Make ITKTestKernel a test dependency

When ITK is compiled with the ITKUltrasound remote module with testing
enabled (e.g. -DModule_Ultrasound=ON -DBUILD_TESTING=ON) the Ultrasound
test driver previously failed to find the itkTestingMacros.h header.

With this change ITKTestKernel is now a test dependency so that the test
driver can be built appropriately when "test/" is not built as a
subdirectory of the root Ultrasound directory.

KitwareMedical/ITKUltrasound,KitwareMedical/ITKUltrasound,KitwareMedical/ITKUltrasound