Volume names have now format <cluster-name>-dynamic-<pv-name>.
pv-name is guaranteed to be unique in Kubernetes cluster, adding
<cluster-name> ensures we don't conflict with any running cluster
in the cloud project (kube-controller-manager --cluster-name=XXX).
'kubernetes' is the default cluster name.
This synchronizes Cinder with AWS EBS code, where we already tag volumes with
claim.Namespace and claim.Name (and pv.Name, as suggested in separate PR).
