Add the description for the following items
in the API reference and the API guide.
* 'X-Openstack-Request-Id' header in request
* 'X-Openstack-Request-Id' header in response
* 'X-Compute-Request-Id' in response
Change-Id: Idd9181c1530eb9576da9941416b697a97c0cfb8d
Closes-Bug: #1693555