Add script to bootstrap installation of `ansible`
Allow customizing the `edx_sandbox.yml` playbook via `site_vars.yml`.

The provided `site_vars.yml` is used for installing edX "siloes"
in the GC3/S3IT "Hobbes" cloud.

  modified:   roles/edxlocal/defaults/main.yml
  modified:   roles/edxlocal/tasks/main.yml
roles/edxlocal: Allow customizing MySQL admin password.

  modified:   roles/edxlocal/defaults/main.yml
  modified:   roles/edxlocal/tasks/main.yml
  new file:   roles/edxlocal/templates/my.cnf.j2
Add playbook to install an edX "silo" on the GC3/S3IT cloud "Hobbes"

The playbook `edx_uzh.yml` runs on a vanilla Ubuntu 12.04 VM where
ansible has been installed (e.g. with the `install-ansible.sh` script),
and:

* upgrades system packages
* sets up the mailer to use UZH `smtp.uzh.ch` for relay
* chain-loads the `edx_sandbox.yml` playbook to complete installation.