conf: Deprecate 'default_floating_pool'

With the advent of the '[neutron] default_floating_pool' option in
I2ce8ff3, it is no longer necessary to keep this option around for
neutron. Burn it. Burn it with fire.

Change-Id: Ib3a64ed297592778c08587af821a832dee11327f
Implements: blueprint centralize-config-options-pike

nova/conf/floating_ips.py

@@ -19,6 +19,14 @@ from oslo_config import cfg
 floating_ip_opts = [
     cfg.StrOpt('default_floating_pool',
         default='nova',
+        deprecated_for_removal=True,
+        deprecated_since='16.0.0',
+        deprecated_reason="""
+This option was used for two purposes: to set the floating IP pool name for
+nova-network and to do the same for neutron. nova-network is deprecated, as are
+any related configuration options. Users of neutron, meanwhile, should use the
+'default_floating_pool' option in the '[neutron]' group.
+""",
         help="""
 Default pool for floating IPs.
 

releasenotes/notes/deprecate-more-nova-network-opts-a9f87c79f7d26438.yaml

@@ -4,6 +4,8 @@ deprecations:
     The following options, found in ``DEFAULT``, were only used for configuring
     nova-network and are, like nova-network itself, now deprecated.
 
+    - ``default_floating_pool`` (neutron users should use the
+      ``neutron.default_floating_pool``)
     - ``ipv6_backend``
     - ``firewall_driver``
     - ``metadata_host``