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.
SIMULATOR: Make enable/disable a setting rather than a message

Closes #121
Update setup.sh

Another test edit.
Merge pull request #157 from fnoble/sim_mode_setting

Make enable/disable a setting rather than a message
Merge pull request #155 from mookerji/ansible-setup22

Ansible setup.sh