run OFP if no application is specified

Keep the old behavior.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Revert "doc: update tls example"

This reverts commit 01dcd0c9bca69d1195504621dda5467e1dfc3c26.
allow RyuApp start() method returns Greenlet thread

This enables an application to continue. Without this, ryu-manager
finishes right after running applications.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofp: use RyuApp start() to return Greenlet thread

starts OFP like other applications. Kill the original way to start OFP
(start_service).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Reviewed-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
rest_router: support OF 1.3

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>