Add Vagrantfile and install script for automatic VM provisioning

This allows creating and launching a virtual machine with a single
command which comes with PyOP2 pre-installed. It requires VirtualBox
4.2 [1] and Vagrant [2] to be installed.

Simply run 'vagrant up' to automatically download the base VM image,
configure it for use with VirtualBox, boot the VM and install PyOP2
and all dependencies. The install script can also be used standalone
outside of the VM context.

[1]: https://www.virtualbox.org/wiki/Linux_Downloads
[2]: http://www.vagrantup.com/
More verbose output
Installer generates a .env script
Install FEniCS dependencies
Allow running as privileged or unprivileged user
Rudimentary check if PyOP2 installed successfully
Pull instead of clone if OP2-Common/PyOP2 repo exists
Properly check whether triangle is installed
Write command output to log file