Added Keystone and RequestID headers to CORS middleware
Added Keystone and RequestID headers to CORS middleware

CORS middleware's latent configuration feature, new in 3.0.0,
allows adding headers that apply to all valid origins.
This patch adds headers commonly used in openstack to heat's paste
pipeline, so that operators do not have to be aware of additional
configuration magic to ensure that browsers can talk to the API.

For more information:
http://docs.openstack.org/developer/oslo.middleware/cors.html#configuration-for-pastedeploy

Change-Id: Ic32d7d2b8d5e1433f806753e94abdc727db07c68

steveb/heat,cwolferh/heat-scratch,dims/heat,dims/heat,jasondunsmore/heat,openstack/heat,noironetworks/heat,openstack/heat,cwolferh/heat-scratch,noironetworks/heat,jasondunsmore/heat,steveb/heat