Verify existing VPC has DNS configured correctly.

[JoshVanL]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

What happened:
Due to a miss-configuration, DNS failed to the vault instances. This meant that tunnels to the vault cluster failed as their address could not be resolved.

What you expected to happen:
We should have a verification for existing VPCs that the DNS is correctly configured.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration**:
• Install tools:
• Others: