Before this PR, CLI functions fatal out when encountering error
instead of returning it. Such behavior makes it hard to reuse
the functions nor writing unit tests. This PR aims to make functions
return errors instead of error out.
Istio sidecar proxy blocks all requests sent through the reverse proxy
to the target service if the request.Host is not properly set to the
internal target service host. This PR sets the target service hosts
before establishing the proxy for the client in order to pass the
Istio sidecar proxy check.
