Add support for x-openstack-request-id

This blueprint is basically the cinder version of the nova blueprint:
https://blueprints.launchpad.net/nova/+spec/cross-service-request-id

---

There is an existing effort to more efficiently trace request flows across OpenStack services. This will be accomplished by logging mappings of request IDs as they cross service boundaries. For example, nova responding to an image-list request will log the request ID of itself along with the request ID it gets back from glance. In this way log info from both sides can be associated.

Since this is dependent on request IDs, there is an effort to standardize the HTTP header used for returning a request ID. This was discussed on openstack-dev: http://lists.openstack.org/pipermail/openstack-dev/2013-December/020774.html

As it stands now, we have glance and neutron using x-openstack-request-id, and nova has a pending change. That just leaves cinder. Cinder is currently using the old nova header name, x-compute-request-id . As with nova and neutron, the plan is to use the already-available request_id oslo middleware to generate the request ID and attach the header.