Update endpoint api for optional region_id
Update endpoint api for optional region_id

As per the bug, 'name' and 'nme' are not part of the 'endpoint'
table and were being assigned to the 'extras' column. This is
why they are not being validated.

The endpoint docs also show that `region_id` is not optional, even
though it is. This updates the docs to reflect optional `region_id`.

Closes-Bug: #1579014
Change-Id: I085b75c59767eb96b3bdfe3b887e5e2639122a34

rajalokan/keystone,rajalokan/keystone,ilay09/keystone,mahak/keystone,ilay09/keystone,ilay09/keystone,mahak/keystone,mahak/keystone,openstack/keystone,rajalokan/keystone,openstack/keystone,openstack/keystone