Regression: of bug 1569299: Version pinning on start

When we added per backend AZs on change I0d7669718a1d1e03e3dd42d1a19b70ff03342bd7 [1] we moved the manager creation to be before the service DB entry creation, ignoring the comments in the code that said this shouldn't be done:

        # NOTE(geguileo): We need to create the Service DB entry before we
        # create the manager, otherwise capped versions for serializer and rpc
        # client would used existing DB entries not including us, which could
        # result in us using None (if it's the first time the service is run)
        # or an old version (if this is a normal upgrade of a single service).

Hence creating a regression, and bringing back bug 1569299 [2] is now back.

Most likely the test added on when fixing the original bug [3] failed to detect the regression.

Original bug text is:

When a service starts (c-sch, c-bak, c-vol) they set the versions for the RPC client and serializer using existing Service entries in the DB, but they don't consider themselves when determining the minimum version.

By not considering themselves we have 2 problematic scenarios:

1- When a service is first started it will pin to None version since there are no Services in the DB
2- When a service is upgraded and restarted it will pin to the old version since the entry in the DB has not been updated yet.

[1]: https://review.openstack.org/#/c/433437/
[2]: https://bugs.launchpad.net/cinder/+bug/1569299
[3]: https://review.openstack.org/#/c/304685/2/cinder/tests/unit/test_service.py