Revert "Issue #181: using virtualenvs for testing singleton in both Python versions"
Revert "Issue #181: using virtualenvs for testing singleton in both Python versions"

This reverts commit ee1ed9b5c879d4730dfc309a31bbf1eb06e4e740.

NifTK/NiftyNet,NifTK/NiftyNet,NifTK/NiftyNet,NifTK/NiftyNet