title: XMLRPC - wp.newPost with custom post type and custom fields
body: <p>I'm trying to add new posts over XMLRPC, but for some reason I cannot add custom fields (other content like title and description works).</p>
  
  <p>Pseudo code that I use:</p>
  
  <pre><code>from xmlrpc import client
  user = 'admin'
  passwd = 'pass'
  server = client.ServerProxy('http://domain.tld/xmlrpc.php')
  blog_id = 0
  
  custom_fields = []
  custom_fields.append(
           {'key' : 'my_meta_key', 'value' : 123}
  )
  
  blog_content = {
      'post_title': title,
      'post_content': content,
      'post_type': 'product',
      'custom_fields': custom_fields
  }
  
  post_id = int(server.wp.newPost(blog_id, user, passwd, blog_content, 0))
  </code></pre>
  
  <p>Posts gets added, however my custom field named <code>my_meta_key</code> is empty.</p>
  
  <p>Cant see what I'm doing wrong. </p>