Make DNS service an agent test...

[a-palchikov]

... and implement DNS service creation in terms of probing Kubernetes API directly (as opposed to using agent test results).

The rationale for this: it is rarely useful to have a system with no DNS kubernetes service. It is entirely possible that DNS service creation fails - this should be one of the agent assertions - i.e. the cluster should be considered degraded if not DNS service has been setup.

How success looks like:

• We have a new agent test that determines if the DNS service has been created
• Planet should use Kubernetes API to create DNS service w/o relying on agent test results