An instance is an abstract container of clusters, it's the cluster that
has the nodes and holds the data, so the number of nodes and location
apply to the cluster.
* govendor fetch cloud.google.com/go/bigtable
* Vendor the rest of the stuff.
* Add support for instance_type to google_bigtable_instance.
* Revendored some packages.
* Removed bad packages from vendor.json