Spec Lite: Actually Deprecate the Glance Registry

problem: A spec to Deprecate the Glance Registry Service was accepted in Newton, but it contained the ambiguous statement, "Mark the service as deprecated and ready for removal in the Q release." It's now the Q release, so we need to actually deprecate it by announcing officially that the Registry Service is deprecated in Queens and subject to removal in the S release.
solution: On startup, the Registry Service should output an appropriate message to the log.
timeline: Q-1 milestone (week of 16 October 2017)
link: https://blueprints.launchpad.net/glance/+spec/deprecate-registry
reviewers: all core reviewers
assignee: rosmaita