some ipv6_only corrections

lib/fog/bluebox/models/compute/server.rb

@@ -92,7 +92,7 @@ module Fog
 
           options['username'] = username
           options['hostname'] = hostname if @hostname
-          options['ipv6_only'] = ipv6_only if @ipv6_only
+          options['ipv6_only'] = ipv6_only if ipv6_only
           data = service.create_block(flavor_id, image_id, location_id, options)
           merge_attributes(data.body)
           true

lib/fog/bluebox/requests/compute/create_block.rb

@@ -30,6 +30,8 @@ module Fog
             'location' => location_id
           }
 
+          query['ipv6_only'] = options.delete('ipv6_only') if options['ipv6_only']
+
           request(
             :expects  => 200,
             :method   => 'POST',