I guess its this route: http://site1.local/app_dev.php/admin/login
You have to make it called "indexAction", when you just wanna call it by http://site1.local/app_dev.php/admin
Explanation:
All routes who access this class go over /admin
If you wanna show content at /admin you have to create "indexAction"
Then all other actions, for example loginAction has /login as route
So you access the class "/admin" and access the loginAction "/login" so its /admin/login/