Add portmap plugin to CNI conf

[osoriano]

Description

The portmap plugin is needed for hostPorts to work

The CNI portmap capability was added in k8s 1.7. I was able to get past the issue by using the updated kube-flannel.yml on a 1.8.3 cluster.

Closes: #887

Release Note

None required

[tomdee]

Looks good

[jethrogb]

10-flannel.conf sorts before 10-flannel.conflist, so if you update you configuration with this change, this change will not be picked up since 10-flannel.conf still exists.

[zcalusic]

I ended up with both 10-flannel.conf & 10-flannel.conflist with the exactly same contents, and lots of kubelet[29256]: W1227 18:53:27.409233 29256 cni.go:125] Error loading CNI config file /etc/cni/net.d/10-flannel.conf: no 'type'; perhaps this is a .conflist? log spam in journal. Every few seconds... :(

Admittedly, this was applied to 0.9.1 image so maybe some bits & pieces are still missing, possibly will be available in 0.9.2?

For now, I deleted 10-flannel.conf, it fixes the extreme log spam issue. Hopefully everything continues working ok...