Treating ErrUnknownPod from ipamd to be a noop

[uruddarraju]

@mogren actually, I dont think this has been fixed yet in the cni, I just saw these logs on the cni agent, after a node reboot, leading to all pods on that node going into an Error status:

2019-12-10T20:00:00.241Z [INFO]         Starting CNI Plugin v1.6.0-rc1-44-g067ddf20 ...
2019-12-10T20:00:00.241Z [INFO]         Received CNI del request: ContainerID(93fb009f691cb1b7d448cf276ddf904ceb562ca5f1f000be8a7c444b0d19cfd2) Netns() IfName(eth0) Args(IgnoreUnknown=1;K8S_POD_NAMESPACE=integration-test-mainst-a0dskoz6ap;K8S_POD_NAME=kube-manager;K8S_POD_INFRA_CONTAINER_ID=93fb009f691cb1b7d448cf276ddf904ceb562ca5f1f000be8a7c444b0d19cfd2) Path(/opt/cni/bin/) argsStdinData({"cniVersion":"0.3.1","mtu":"9001","name":"aws-cni","type":"aws-cni","vethPrefix":"eni"})
2019-12-10T20:00:00.245Z [ERROR]        Error received from DelNetwork grpc call for pod kube-manager namespace integration-test-mainst-a0dskoz6ap container 93fb009f691cb1b7d448cf276ddf904ceb562ca5f1f000be8a7c444b0d19cfd2: rpc error: code = Unknown desc = datastore: unknown pod
2019-12-10T20:00:00.245Z [ERROR]        Failed CNI request: rpc error: code = Unknown des

Issue: #740 and #739

[mogren]

Thanks, I've tested it and it works 😄