ryu-manager: use try-finally statement

This fixes a problem that app_mgr.close() is not called when
KeyboardInterrupt exception occurs.

Signed-off-by: OHMURA Kei <ohmura.kei@lab.ntt.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
app_manager: fix close dict handling bug

Signed-off-by: OHMURA Kei <ohmura.kei@lab.ntt.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>