RF: refactor using explicit paths for python, pip

* Set explicit python and pip path from virtualenv in the hope of
  resolving odd path bugs for the travis build.
* Use delocate without full path (from virtualenv) as the path should
  get picked up from the virtualenv
RF: log messages instead of printing them
RF: remove unused wscript function
RF: add option to force pip install options

Move URL for scipy_installers to install.sh script.