This adds the CORS support middleware to Trove, allowing a deployer
to optionally configure rules under which a javascript client may
break the single-origin policy and access the API directly.
For trove, the paste.ini method of deploying the middleware was
chosen, because it needs to be able to annotate responses created
by keystonemiddleware. If the middleware were explicitly included
as in the previous patch, keystone would reject the request before
the cross-domain headers could be annotated, resulting in an
error response that was unreadable by the user agent.
OpenStack Spec:
http://specs.openstack.org/openstack/openstack-specs/specs/cors-support.html
Oslo_Middleware Docs:
http://docs.openstack.org/developer/oslo.middleware/cors.html
Cloud Admin Guide Documentation:
http://docs.openstack.org/admin-guide-cloud/cross_project_cors.html
Change-Id: Ic55305607e44069d893baf2a261d5fe7da777303
e64cf4bd29