Add virtualenv to Vagrantfile in order to remove sudo

[cristobal23]

Greetings folks!
I offer my suggestions here in this pull request.

• Adding the config.ssh.shell option allows vagrant to start bash as a non-login shell which prevents a stdin: is not a tty error from coming up.
• Removing the commented out sudo apt-get update as the vagrant provisioner only runs when the virtual machine is created unless the option --provision is passed the next time you run vagrant.
• Adding a virtualenv prevents the potential of corrupting system libraries. This layer of separation can be useful even in a sandboxed operating system whether in a virtual machine or a container.
• Speaking of containers, you can achieve a similar sandbox with this command:

docker run -i --rm -v $(pwd):/opt -w='/opt' python:2 /bin/bash -c "virtualenv venv && source venv/bin/activate && pip install -e ."

Please let me know what you think about these suggestions.

[yuhunglin]

@cristobal23 This looks good, thanks for the suggestions, feel free to chime in on other elements as well.