New API for WebSocket support

- API
 - @websocket decorator
 - WSGIApplication#websocketmanager()
- bugfix
 - Even if a connection is cut, it continues remaining
- remove restriction
 - Two or more connections can be accepted

Signed-off-by: Satoshi Kobayashi <satoshi-k@stratosphere.co.jp>
Reviewed-by: YAMADA Hideki <yamada.hideki@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
simple_switch_websocket_13: fix typo

Signed-off-by: YAMADA Hideki <yamada.hideki@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Add WebSocket JSON RPC feature

Signed-off-by: YAMADA Hideki <yamada.hideki@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
pip-requires: WebSocket-RPC requires tinyrpc

Signed-off-by: YAMADA Hideki <yamada.hideki@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
simple_switch_websocket_13: Add get_arp_table RPC method

Signed-off-by: YAMADA Hideki <yamada.hideki@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
sw test tool: support fluctuations of sending

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>