CLI-related make goals are confusing

[pires]

• get-cli downloads kubectl and dcos to the working directory. It never checks if the binaries are already available, if the version matches, etc. before downloading, so every call downloads the binaries to the working directory.
• setup-cli calls dcos from the working directory. It doesn't check if the binary is available, if the version matches, etc.

Then, references to kubectl always assume that kubectl is available in $PATH. If that's the case, we may end up with a kubectl v1.7.x in $PATH being called to interact with Kubernetes 1.10.3, even after get-cli downloaded kubectl v1.10.3 to the working directory.

I ran into this just now and it was painful to figure out.

My suggestion is to keep thing simple and just check for dcos and kubectl in $PATH, and show a warning about potential conflicts if their versions don't match the server-side versions.

[rimusz]

yes, we do need to handle it in a better way