Created the admin directory, remove some files from
user dir and placed into admin and contributor.

For more detail, see the doc migration spec.
http://specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration.html

Change-Id: I84c565d7d14a4d90270a53e14ab93a10f7ffb9b7
Partially-Implements: blueprint ka-queens-doc-restructure