Clarify assignment of LLC CLA rights

* modules/openstack_project/files/gerrit/cla.html: The language
for assigning the rights and obligations of any previous agreement
with OpenStack, LLC needed to be clarified to express how the
parties to the prior agreement would transfer the agreement to
OpenStack Foundation

Change-Id: Icb6aad43426f6fb3c29d78cb8f3de652cdf6598e
Reviewed-on: https://review.openstack.org/22910
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins