Update docs.o.o/trunk/index for new manuals

I've added a new section "Use an OpenStack Cloud" and added all manuals.

All URLs should point to current building books - but some book URL
might need to be changed.

I expect that the following URLs will change:
http://docs.openstack.org/cloud-admin/admin-guide-cloud/admin/content/
http://docs.openstack.org/trunk/image-guide/content/

Change-Id: Ib9e41be6b5085635ba193665730e1903bc9de15f
Merge "Update docs.o.o/trunk/index for new manuals"