add provider specific removePrivateFields to redact tokens and secrets

src/dns/gcdns.js

@@ -1,6 +1,7 @@
 'use strict';
 
 exports = module.exports = {
+    removePrivateFields: removePrivateFields,
     upsert: upsert,
     get: get,
     del: del,
@@ -18,6 +19,11 @@ var assert = require('assert'),
     waitForDns = require('./waitfordns.js'),
     _ = require('underscore');
 
+function removePrivateFields(domainObject) {
+    domainObject.config.credentials.private_key = domains.SECRET_PLACEHOLDER;
+    return domainObject;
+}
+
 function getDnsCredentials(dnsConfig) {
     assert.strictEqual(typeof dnsConfig, 'object');