The vtk_(add|module)_library macros set the OUTPUT_NAME property of the
target to add the VTK version number to the library file name.  Since
commit 1494cdd4 (Add python version numbers only to files, 2012-06-12)
we set the OUTPUT_NAME property of VTK Python library targets to add the
python version number, accidentally dropping the VTK version number.

Add the python version number by getting the OUTPUT_NAME property
value already set by vtk_add_library and replacing "Python" with
"Python${XY}".  Then set the OUTPUT_NAME property with the result.

Change-Id: Ie7ff1268162b077f7bd543df4b785dd49f1be02f