Update api-ref location

The api documentation is now published on docs.openstack.org instead
of developer.openstack.org. Update all links that are changed to the
new location.

Note that redirects will be set up as well but let's point now to the
new location.

For details, see:
http://lists.openstack.org/pipermail/openstack-discuss/2019-July/007828.html

Change-Id: Ib854afe939791180153cccc4b0313e5b25842f7e
14 files changed