Enable inter-nodegroup DNS access

[errordeveloper]

Description

With the introduction of multi-nodegroup support, we have missed the fact that node ports below 1025 are not open (accept for 22 being controller by --ssh-access, and 443 being open only to the EKS control plane). We might need to widen internal port access in the future (see #419), but for now we have to open DNS port, as it cripples the functionality of a multi-nodegroup cluster.

Fixes #414.

For discussion of full stricter isolation, see #417.

Checklist

• Code compiles correctly (i.e make build)
• Added tests that cover your change (if possible)
• All tests passing (i.e. make test)
• Provide path for users with broken nodegroups - will do in another PR