Add check for orphaned UsersGroups

lib/tasks/gitlab/check.rake

@@ -17,6 +17,7 @@ namespace :gitlab do
       check_database_config_exists
       check_database_is_not_sqlite
       check_migrations_are_up
+      check_orphaned_users_groups
       check_gitlab_config_exists
       check_gitlab_config_not_outdated
       check_log_writable
@@ -181,6 +182,15 @@ namespace :gitlab do
       end
     end
 
+    def check_orphaned_users_groups
+      print "Database contains orphaned UsersGroups? ... "
+      if UsersGroup.where("user_id not in (select id from users)").count > 0
+        puts "yes".red
+      else
+        puts "no".green
+      end
+    end
+
     def check_satellites_exist
       print "Projects have satellites? ... "