Allow option to disable Swift ring management

Allow option to disable Swift ring management

There are quite a few cases where it is useful to disable ring building on the
nodes. For example:

- using different weights, regions, and zones
- replacing a node in an existing Swift cluster
- adding a new node to an existing cluster
- using storage policies and therefore multiple rings
- using different nodes and disks for account, container and object servers

This patch allows it to disable ring building. Rings need to be maintained
manually then, and copied to all storage and proxy nodes within a cluster.

This patch is similar to I01311ec3ca265b151f8740bf7dc57cdf0cf0df6f, except that
it uses the current templates.

Change-Id: I56978b15823dd6eaf4b6fd3440df2f895e89611a