Currently, cli/cmd/root.go provides a couple of utilities for building
clients to Linkerd's Public API; however these utilities are infallible,
execute health checks, etc.
There are a class of API clients---for instance, when an inject command
wants to acquire configuration from the API---where these checks are
undesirable. The version CLI built such a client, for example.
This change consolidates the various utilities into a single file.
Furthermore, it renames these utilities to clarify they differ.