Make VM smaller: switch VCM to Python3

[riebling]

With a few code changes, VCM can use Python3 (in the virtualenv named 'divime' installed at provision time, configured by environment.yml) specifically the Torch package installed already there for Yunitator & Noisemes to use... thus eliminating the need to install Torch twice (once for Python2, once for Python3).

This will make the VM slightly smaller & faster to set up. Slightly.

Things that'd have to happen:

• source activate divime in the VCM run script
• don't change PATH in VCM run script
• switch python2 to python3 in the VCM run script
• add the gerbils, I mean pandas package to environment.yml (needed by vcm)
• eliminate the lines in bootstrap.sh that install torch and cuda