Improve Log Handling

[dave-tucker]

The current client discards output from anybody using the global log instance.

 log.SetOutput(ioutil.Discard)

Once this is removed, a better logging solution should be put in place such that the client can either use a pointer to a global logger (e.g one provided by an external framework that adheres to the Logger API) or the global log.Logger).

Prompts like this should be purged from stdout, so the logging style is consistent.

==> Starting Consul agent...