COMP: Do not pip install --upgrade virtualenv packages.
COMP: Do not pip install --upgrade virtualenv packages.

Python lacks a decent build system and can easily fail to build.

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