Updates to provisioning script.

0. Updated version of Ubuntu used in Vagrant test.
1. Fix for Ubuntu install.
Moves setup.sh dependency provisioning to Ansible.

Replaces the error-prone bash script provisioning in OS X and Linux
with an Ansible playbook, which has clearer error messages/handling,
and will hopefully be more reproducible across machines.

r=@kovach,@fnoble,@cbeighley
Updated README.md to reflect setup.sh change.
Refactoring arm entry point.
Conditional arm installation.
Clarifying comments for provisioning script.
Removing USB configuration from Vagrantfile.

USB enabling requires a VirtualBox plugin that not everyone might
have, causing `vagrant up` to fail.
Modified Homebrew install and unlinking swig in setup script.
Moved the Homebrew path up for Python installation.
Remove error logging from homebrew swig installation.
Proper ansible command for piping.
Merge pull request #155 from mookerji/ansible-setup22

Ansible setup.sh