ghost_head improvements (#8983)

no issue

- Added debug statements to ghost_head
  - useful for determining how much render time is spent in ghost head
- Make promises more readable
- Used join instead of props for less code

core/server/helpers/ghost_head.js

@@ -9,6 +9,7 @@
 var proxy = require('./proxy'),
     _ = require('lodash'),
     Promise = require('bluebird'),
+    debug = require('ghost-ignition').debug('ghost_head'),
 
     getMetaData = proxy.metaData.get,
     getAssetUrl = proxy.metaData.getAssetUrl,
@@ -24,7 +25,9 @@ var proxy = require('./proxy'),
 
 function getClient() {
     if (labs.isSet('publicAPI') === true) {
-        return api.clients.read({slug: 'ghost-frontend'}).then(function (client) {
+        return api.clients
+            .read({slug: 'ghost-frontend'})
+            .then(function handleClient(client) {
                 client = client.clients[0];
 
                 if (client.status === 'enabled') {
@@ -80,30 +83,26 @@ function getAjaxHelper(clientId, clientSecret) {
 }
 
 module.exports = function ghost_head(options) {
+    debug('begin');
     // if server error page do nothing
     if (this.statusCode >= 500) {
         return;
     }
 
-    var metaData,
-        client,
-        head = [],
+    var head = [],
         globalCodeinjection = settingsCache.get('ghost_head'),
         postCodeInjection = options.data.root && options.data.root.post ? options.data.root.post.codeinjection_head : null,
         context = this.context ? this.context : null,
         useStructuredData = !config.isPrivacyDisabled('useStructuredData'),
         safeVersion = this.safeVersion,
         referrerPolicy = config.get('referrerPolicy') ? config.get('referrerPolicy') : 'no-referrer-when-downgrade',
-        fetch = {
-            metaData: getMetaData(this, options.data.root),
-            client: getClient()
-        },
         favicon = blogIconUtils.getIconUrl(),
         iconType = blogIconUtils.getIconType(favicon);
 
-    return Promise.props(fetch).then(function (response) {
-        client = response.client;
-        metaData = response.metaData;
+    debug('preparation complete, begin fetch');
+    return Promise
+        .join(getMetaData(this, options.data.root), getClient(), function handleData(metaData, client) {
+            debug('end fetch');
 
             if (context) {
                 // head is our main array that holds our meta data
@@ -167,9 +166,12 @@ module.exports = function ghost_head(options) {
                 }
             }
             return filters.doFilter('ghost_head', head);
-    }).then(function (head) {
+        })
+        .then(function afterFilters(head) {
+            debug('end');
             return new SafeString(head.join('\n    ').trim());
-    }).catch(function handleError(err) {
+        })
+        .catch(function handleError(err) {
             logging.error(err);
 
             // Return what we have so far (currently nothing)