MS: Align HTML structure in `wp-signup.php` and `wp-activate.php`.

Assigns the `wp-activate-container` and `wp-signup-container` to the container inside `#signup-container` on each. This container already existed in `wp-signup.php` and is new in `wp-activate.php`.

Props ocean90.
Fixes #25478.


git-svn-id: https://develop.svn.wordpress.org/trunk@34814 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-activate.php

@@ -68,6 +68,7 @@ get_header();
 ?>
 
 <div id="signup-content" class="widecolumn">
+	<div class="wp-activate-container">
 	<?php if ( empty($_GET['key']) && empty($_POST['key']) ) { ?>
 
 		<h2><?php _e('Activation Key Required') ?></h2>
@@ -127,6 +128,7 @@ get_header();
 		}
 	}
 	?>
+	</div>
 </div>
 <script type="text/javascript">
 	var key_input = document.getElementById('key');

src/wp-signup.php

@@ -76,7 +76,7 @@ get_header();
 do_action( 'before_signup_form' );
 ?>
 <div id="signup-content" class="widecolumn">
-<div class="mu_register">
+<div class="mu_register wp-signup-container">
 <?php
 /**
  * Generates and displays the Signup and Create Site forms