- What I did
This pull request adds the Stack API resolution mechanism and print the selected version into the version command. It lays the foundation for a following one #899, which adds the v1beta2 version of the Stack API. It's extracted from the PR #854 .

- How I did it

• Resolve Stack API using Kubernetes discovering API
• Refactor Kubernetes flags parsing

- How to verify it
Execute a docker version command against latest docker for mac, it should output at the end:

 Orchestrator:
   Kubernetes:  v1.9.2
   Stack:       v1beta1

- Description for the changelog

• Add Stack API and Kubernetes versions in version command

- A picture of a cute animal (not mandatory but encouraged)