adapted to kubernetes scheduling plugin api

Deploying a pod JSON works again, though I get an error at the client side (even though the pod deploys OK):

    [root@mesos-dev k8s-mesos]# curl -L http://localhost:8080/api/v1beta1/pods -XPOST -d @nginx.json
    {"kind":"Status","creationTimestamp":null,"apiVersion":"v1beta1","status":"failure","message":"Could not resolve pod 'nginx-id-01' to task id","code":500}