Refer multi node install to docs.openstack.org

The multi-node install was so horribly outdated it still
refered to ubuntu 10.04. The install guide at docs.openstack.org
has a usable swift installation guide - link to it until such
time as this page can be fixed.

Change-Id: I29fa334d9ffc9b63c8f31c664e7509b2f2577574