Related to #2309, this allows naming an existing key pair using the
cluster spec field `sshKeyName`.
In our use case, kops can now be used without providing the ability to
create EC2 key pairs.
Added:
- Instance role name
- Instance role arn
as terraform outputs, this can then be references later on to
use as sts:assume role, create after this one
* Zones are now subnets
* Utility subnet is no longer part of Zone
* Bastion InstanceGroup type added instead
* Etcd clusters defined in terms of InstanceGroups, not zones
* AdminAccess split into SSHAccess & APIAccess
* Dropped unused Multizone flag