Use Vagrant's Ansible provisioner

Use Vagrant's built-in support for Ansible provisioner. This eliminates the need
for a hosts file, and simplifies the ansible config file.

Renames config from .ansible.cfg to ansible.cfg since Ansible expects the file
to be called ansible.cfg and be adjacent to Vagrantfile when using the Vagrant
provisioner.
Merge pull request #82 from lorin/master

Use Vagrant's Ansible provisioner