Merge branch 'ldap_user_attr_method' into 'master'

Move LDAP user attributes to a method

## What does this MR do?

This is a change that supports an EE fix. This small change needs to be made in CE to prevent future merge conflicts. 
See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/736 for the EE changes.

See merge request !6377

lib/gitlab/ldap/adapter.rb

@@ -70,7 +70,7 @@ module Gitlab
       private
 
       def user_options(field, value, limit)
-        options = { attributes: %W(#{config.uid} cn mail dn) }
+        options = { attributes: user_attributes }
         options[:size] = limit if limit
 
         if field.to_sym == :dn
@@ -98,6 +98,10 @@ module Gitlab
           filter
         end
       end
+
+      def user_attributes
+        %W(#{config.uid} cn mail dn)
+      end
     end
   end
 end