Accomodate redhat client

Patch from @jk at https://forum.cloudron.io/topic/4383/cannot-install-apps-from-docker-registry-because-authentication-fails

src/nginxconfig.ejs

@@ -275,6 +275,9 @@ server {
         if ($http_user_agent ~* "docker") {
             return 401;
         }
+        if ($http_user_agent ~* "container") {
+            return 401;
+        }
         return 302 /login?redirect=$request_uri;
     }