adjust import order in ryu-manager and add a comment.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
update a sample and documentation

try to sync the documentation with the reality at least about
gflags/cfg changes.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
fix a typo in the help message of quantum_controller_addr

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
stop requiring gflags

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>