STYLE: Set SlicerExecutionModel output dir based on install dir
STYLE: Set SlicerExecutionModel output dir based on install dir

This will allow to easily customize the build output directory by
simply changing the install directory.

aylward/ITKTubeTK,sumedhasingla/TubeTK,KitwareMedical/ITKTubeTK,cdeepakroy/TubeTK,thewtex/TubeTK,cdeepakroy/TubeTK,sumedhasingla/TubeTK,KitwareMedical/TubeTK,aylward/ITKTubeTK,KitwareMedical/ITKTubeTK,sumedhasingla/TubeTK,KitwareMedical/TubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/TubeTK,KitwareMedical/TubeTK,cdeepakroy/TubeTK,sumedhasingla/TubeTK,KitwareMedical/ITKTubeTK,thewtex/TubeTK,aylward/ITKTubeTK,cdeepakroy/TubeTK,thewtex/TubeTK,aylward/ITKTubeTK,thewtex/TubeTK