Deprecate Cinder Hosts API/Extension

This was added a long long long long time ago, but it was never
fully implemented and is not used anywhere.  It might be worth
resurrecting and having, but it should probably be a first class
API rather than an extension, and if nothing else it would be good
if we want this to create a spec and have a real plan on it's
implementation and usage.

Bottom line, it's not used anywhere and the implementation is not
complete.  We could probably remove it safely, but let's deprecate
it and fast track removal and possible replacement next cycle.

Change-Id: I1a1920d141c8c32a8fb30bc6f73e955a1a1c5150

cinder/api/contrib/hosts.py

@@ -17,6 +17,7 @@
 
 from oslo_config import cfg
 from oslo_log import log as logging
+from oslo_log import versionutils
 from oslo_utils import timeutils
 import webob.exc
 
@@ -89,6 +90,10 @@ class HostController(wsgi.Controller):
     def __init__(self):
         self.api = volume_api.HostAPI()
         super(HostController, self).__init__()
+        versionutils.report_deprecated_feature(
+            LOG,
+            "The Host API is deprecated and will be "
+            "be removed in a future version.")
 
     def index(self, req):
         context = req.environ['cinder.context']

releasenotes/notes/deprecate_hosts_api_extension-fe0c042af10a20db.yaml

@@ -0,0 +1,9 @@
+---
+upgrade:
+  - |
+    The hosts api extension is now deprecated and will be removed in a
+    future version.
+deprecations:
+  - |
+    The hosts api extension is now deprecated and will be removed in a
+    future version.