Steps to reproduce the issue

1. Create menu item for "Login form" (alias: login)
2. In "Metadata" tab, set "Robots" field to "No index, no follow"
3. Go to http://www.example.com/login (Created item)
4. View source

Expected result

<meta robots=robots content="noindex, nofollow"/> should be present.

Actual result

It is not.

System information (as much as possible)

• Multilingual enviroment
• PHP 7.1.2
• Apache 2.4.6
• Joomla 3.6.5
• SEF URLs: yes
• URL rewriting: yes
• Unicode Aliases: yes
• Cache: On - Progressive

Additional comments

It's solved by modifying line 128 of "components/com_users/views/login/view.html.php":

$this->document->setMetaData('robots', $this->params->get('robots'), 'robots');