Merge branch 'ldap_fix_api' into 'master'

Fix bad Group class resolution when querying LDAP via API

When querying LDAP groups via the API, there was a 500 error with a strange stack. Thanks to @DouweM we figured out that in the context of the API, it's choosing `::Group` instead of `EE::Gitlab::LDAP::Group`. This makes it just specific enough to work. 

See merge request !572

lib/ee/gitlab/ldap/adapter.rb

@@ -22,7 +22,7 @@ module EE
           options.merge!(size: size) if size
 
           ldap_search(options).map do |entry|
-            Group.new(entry, self)
+            LDAP::Group.new(entry, self)
           end
         end