错误现象:
untime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni config uninitialized

解决办法:
手动添加 flannel 镜像和 cni 配置

docker pull quay.io/coreos/flannel:v0.11.0-amd64

mkdir -p /etc/cni/net.d/

cat <<EOF> /etc/cni/net.d/10-flannel.conf
{"name":"cbr0","type":"flannel","delegate": {"isDefaultGateway": true}}
EOF

mkdir /usr/share/oci-umount/oci-umount.d -p

mkdir /run/flannel/

cat <<EOF> /run/flannel/subnet.env
FLANNEL_NETWORK=172.100.0.0/16
FLANNEL_SUBNET=172.100.1.0/24
FLANNEL_MTU=1450
FLANNEL_IPMASQ=true
EOF