Consider Rancherizing Aegir

We could come up with a Rancher implementation for Aegir based on the following:

• http://rancher.com/
• https://github.com/jonpugh/aegir-rancher-stack

The following issues are prerequisites:

• #2770077: RFC: Refactor how Aegir installs Drupal.
• #2764245: Refactor PROVISION_SITE_INSTALLED to be more verbose and actually check if site was installed.
• #2754069: API Only: Allow site nodes to specify "install_method", allowing something other than automated Drupal profile.
• #2704799: RFC: Add a 'distribution' content type

See also: https://github.com/opendevshop/devshop_rancher