Add a cheeky ping check to the new API.

I've opened this PR against `cdm-0.3.0` although it builds on the work in `cdm-0.3.0-kv-listing`. Please review (first): https://github.com/orchestrate-io/orchestrate-java-client/pull/28

We can replace this with a better ping check operation when it's supported in the Orchestrate API.

@housejester ping :smiley: