Use uuids in services and os-hypervisors APIs

We currently leak database id fields (primary keys) out of the compute REST API for services and compute_nodes which are all in a cell database (the 'nova' database in a cells v2 deployment). These are in the os-services and os-hypervisors APIs, respectively.

For example, to delete a service record, you must issue a DELETE request to /os-services/{service_id} to delete the service record with that id.

The os-hypervisors API exposes the id in GET (index) requests and uses it in the "show" and "uptime" methods to look up the ComputeNode object by that id.

This is gross but functional in a single-cell deployment. However, in a multi-cell deployment, we have no context on which cell we should query to get service/node details from, since you could have multiple cells each with a nova-compute service and compute node with id 1, so which cell do you pick to delete the service or show details about the hypervisor?

This blueprint proposes to add a microversion to the compute REST API which replaces the usage of the id field with a uuid field. The uuid would be returned instead of the id in GET responses and also taken as input for the id in CRUD APIs.

Then when a request to delete a service is made, if the uuid is provided we can simply iterate cells until we find the service, or error with a 404.

Before the microversion, if an id is passed and there is only one cell, or no duplicates in multiple cells, we'll continue to honor the request. But if an id is passed on the request (before the microversion) and we cannot uniquely identify the record out of multiple cells, we error with a 400. This is similar behavior to how creating a server works when a network or port is not provided and there are multiple networks available to the project, we fail with a 400 "NetworkAmbiguous" error.

The compute_nodes table already has a uuid field. The services table, however, does not, so as part of this blueprint we'll need to add a uuid column to that table and corresponding versioned object.