[Hui Xiang] Replace 'use-ipv6' with 'prefer-ipv6'.

config.yaml

@@ -133,7 +133,7 @@ options:
       description: |
         Key ID to import to the apt keyring to support use with arbitary source
         configuration from outside of Launchpad archives or PPA's.
-  use-ipv6:
+  prefer-ipv6:
     type: boolean
     default: False
     description: "Enable Ipv6"  

hooks/rabbitmq_server_relations.py

@@ -116,7 +116,7 @@ def amqp_changed(relation_id=None, remote_unit=None):
                     queues[amqp]['username'],
                     queues[amqp]['vhost'])
 
-    if config('use-ipv6'):
+    if config('prefer-ipv6'):
         relation_settings['hostname'] = '[%s]' % get_ipv6_addr()
     else:
         relation_settings['hostname'] = unit_get('private-address')
@@ -533,7 +533,7 @@ def config_changed():
     chown(RABBIT_DIR, rabbit.RABBIT_USER, rabbit.RABBIT_USER)
     chmod(RABBIT_DIR, 0o775)
 
-    if config('use-ipv6'):
+    if config('prefer-ipv6'):
         rabbit.bind_ipv6_interface()
 
     if config('management_plugin') is True: