Upgrade Vagrantfile and playbook for Ansible 1.5.5/Vagrant 1.6.

Changes include syntax update for site.yml using new Jinja2-style
variables and make Vagrant provision to all hosts rather than single
host with limit all.
Change to run uWSGI with supervisor instead of upstart.

So all our Python processes (and Node process) are running in the
consistent manner with Supervisord. This allow overall easier
process management.
Merge branch 'feature/ansible-upgrade' into develop