Rearrange certificates response schema into one file

After removing v3 schemas, we have only 1 set of schemas for v2 (/v2.1)
APIs but those end up in scattered structure.

Schema files needs to be re arranged into a clean structure. Any
resource schema should be defined in single file for better readability.

This patch merge the certificates response schema into one file.

Partially implements blueprint rearrange-nova-response-schemas

Change-Id: I50752ca74f08029c16913bea98361d84d04aa90c
3 files changed