COMP: Fix project linking against ITK that does not use VtkGlue.

The problem:

ITK is built with the ITKVtkGlue or ITKLevelSetsv4Visualization module enabled.
A project that uses ITK, but does not use VTK, does a

find_package(ITK REQUIRED)
include(${ITK_USE_FILE})

but if the VTK_DIR that was specified for ITKVtkGlue is at a build tree
location, CMake does not know where to find the VTK libraries.

The solution:

In the per-VTK-module export code, we should include VTKTargets.cmake so CMake
knows where to find the VTK libraries.  To do so, run find_package(VTK_DIR
NO_MODULE REQUIRED) with the VTK_DIR used during ITK configuration.

Change-Id: I6c74891f97da80c1b1ac352b8f7495439c80d610
Merge topic 'LinkVTKGlueNotUsed'

4371df2 COMP: Fix project linking against ITK that does not use VtkGlue.