docker_base.py: fix an ip option of "docker network connect"
docker_base.py: fix an ip option of "docker network connect"

ip address with subnet is ignored in ip option of "docker network connect"
This patch specifies a correct ip format for option.

Signed-off-by: Fumihiko Kakuma <f97de62a9424cc14113f997adeee0fdcdc9c7694@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

shinpeimuraoka/ryu,iwaseyusuke/ryu,fujita/ryu,lagopus/ryu-lagopus-ext,osrg/ryu,shinpeimuraoka/ryu,lagopus/ryu-lagopus-ext,gareging/SDN_Framework,gareging/SDN_Framework,shinpeimuraoka/ryu,iwaseyusuke/ryu,gareging/SDN_Framework,gareging/SDN_Framework,fujita/ryu,iwaseyusuke/ryu,osrg/ryu,gareging/SDN_Framework,lagopus/ryu-lagopus-ext,fujita/ryu,shinpeimuraoka/ryu,fujita/ryu,osrg/ryu,lagopus/ryu-lagopus-ext,fujita/ryu,iwaseyusuke/ryu,shinpeimuraoka/ryu,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,osrg/ryu,osrg/ryu