topology/dumper: use handler.set_ev_cls instead of set_ev_handler

There is no point for dumper.py to use handler.set_ev_cls.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ryu/base/app_manager: pylint unused variables

pylint fix

> W:201,12:AppManager.instantiate_apps: Unused variable 'key'
> W:222,24:AppManager.instantiate_apps: Unused variable 'handler'

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
base/app_manager.py: sort out registering bricks

When registering RyuApps to observers with _EVENTS,
it should applied to @set_ev_cls methods, and dispatchers should be
honored.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ryu/base/app_manager: introduce RyuApp:replay_to_request()

This is a handy method for event request/reply.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ryu/topology/switches: simplify Switches with RyuApp.reply_to_request

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>