Assert default project id is not domain
Assert default project id is not domain

If using default project id when creating user, make sure
the project is not a domain.
This patch add the note to the description of default_project_id
in api ref.

Change-Id: Iedda6df116f237cb68a882efff6f3e19c6ee8e72

mahak/keystone,mahak/keystone,mahak/keystone,openstack/keystone,openstack/keystone,openstack/keystone