Detect virtualenvwrapper exe

[DonJayamanne]

We detect the environments, but not the exe.
Shoudl be possible to spawn and find this.

https://virtualenvwrapper.readthedocs.io/en/latest/install.html#python-interpreter-virtualenv-and-path

To override the $PATH search, set the variable VIRTUALENVWRAPPER_PYTHON to the full path of the interpreter to use and VIRTUALENVWRAPPER_VIRTUALENV to the full path of the virtualenv binary to use. Both variables must be set before sourcing virtualenvwrapper.sh. For example:

export VIRTUALENVWRAPPER_PYTHON=/usr/local/bin/python
export VIRTUALENVWRAPPER_VIRTUALENV=/usr/local/bin/virtualenv
source /usr/local/bin/virtualenvwrapper.sh