Replace the JSON round-trip with #stringify.

Let's use a proper method to emulate what round-tripping data structures
through the JSON API will do.

lib/fog/rackspace/mock_data.rb

@@ -232,6 +232,23 @@ module Fog
       def self.zulu_time
         Time.now.strftime("%Y-%m-%dT%H:%M:%SZ")
       end
+
+      def self.stringify(message)
+        case message
+        when Symbol
+          message.to_s
+        when Hash
+          result = Hash.new
+          message.each do |key, value|
+            nk = stringify(key)
+            nv = stringify(value)
+            result[nk] = nv
+          end
+          result
+        else
+          message
+        end
+      end
     end
   end
 end

lib/fog/rackspace/requests/queues/create_message.rb

@@ -39,10 +39,10 @@ module Fog
 
           raise BadRequest.new if body.nil? || body.empty?
 
-          # Round-trip +body+ through the JSON parser to turn Symbols into Strings, as though
-          # it's coming back from the server.
-          encoded = Fog::JSON.decode(Fog::JSON.encode(body))
-          message = queue.add_message(client_id, encoded, ttl)
+          # Ensure that any Symbol keys within +body+ are converted to Strings, just as being
+          # round-tripped through the API will.
+          converted = MockData.stringify(body)
+          message = queue.add_message(client_id, converted, ttl)
 
           response = Excon::Response.new
           response.status = 201