Update README
Update README

The CloudKeep organization was removed from GitHub for unknown
reasons.  This patch removes any mention of a CloudKeep project
as they were all vaporware anyway.

Also fixed the python-barbicanclient to point to opendev.org as
it is the official repo, and the reop at github.com is a mirror.

Change-Id: If45f75b0c0e7bbab0c0a74fb9a027ad87068a7f1

openstack/barbican,openstack/barbican