Write a kubernetes module in the jelastic-client package

[zadigus]

We need a little module with one function that allows to connect to a deployed kubernetes cluster. The function performs following actions:

kubectl config set-cluster ${CLUSTER_NAME} --server=${API_ENDPOINT}
kubectl config set-context ${CLUSTER_NAME} --cluster=${CLUSTER_NAME}
kubectl config set-credentials ${CLUSTER_USERNAME} --token=${TOKEN}
kubectl config set-context ${CLUSTER_NAME} --user=${CLUSTER_USERNAME}
kubectl config use-context ${CLUSTER_NAME}