contrib: import ncclient library (NETCONF clients)

NETCONF clients

https://github.com/leopoul/ncclient/

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
contrib ncclient: missing comma

comma(",") is missing.

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