* Stop setting the Name tag on a shared subnet/vpc
* Stop setting the legacy KubernetesCluster tag on a shared subnet/vpc
that is new enough (>=1.6); we rely on the shared tags instead
* Set tags on shared subnets; i.e. we _do_ set the shared tag on a
shared subnet; that is important for ELBs
* Set tags on shared VPCs; i.e. we _do_ set the shared tag on a shared
VPC; that is not used but consistent with subnets.
* Add tests for shared subnet