Update docs.o.o footer to current www.o.o content
Update docs.o.o footer to current www.o.o content

The main website footer fixed a link, introduced a new one and
now credits Vexxhost for hosting resources -- the docs.openstack.org
footer needs to be updated to match.

Change-Id: Ia2f60661e6ed1eedb73886731e2143bae012b043

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals