config_by_role calls to use "openstack-identity"

config_by_role seeks to search for a node with a specific role and
then key into specific parts of its attribute structure. As the name
of the identity cookbook has changed to openstack-identity, we need
to key into the tree appropriately.

Change-Id: Id23ae4d3947b62f11a2c8c40cad2a06c42dc303a