Make the JSON RPC server work with both IPv4 and IPv6

Binding to 0.0.0.0 by default results in inability to work with IPv6,
which is a probable cause of Bifrost gate failures on some nodepool
providers. Using :: solves it.

Change-Id: Ic5c4c9b541c826ccf3025877f7c829fd34d0be6e

ironic/conf/json_rpc.py

@@ -23,7 +23,7 @@ opts = [
                help=_('Authentication strategy used by JSON RPC. Defaults to '
                       'the global auth_strategy setting.')),
     cfg.HostAddressOpt('host_ip',
-                       default='0.0.0.0',
+                       default='::',
                        help=_('The IP address or hostname on which JSON RPC '
                               'will listen.')),
     cfg.PortOpt('port',

releasenotes/notes/json-rpc-bind-a0348cc6f5efe812.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The internal JSON RPC server now binds to ``::`` by default, allowing it to
+    work correctly with IPv6.