Allow user to override the Go server host via an attribute

This allows both chef-solo _and_ chef-client to set the Go server host IP. Chef-client will also output warnings if it can't find a Go server or if it finds more than one. If all else fails fall back on 127.0.0.1 as the Go server IP.

The Go server search query for chef-client is an attribute now. This lets wrapper cookbooks override the search criteria that works for their environment. In our infrastructure our Go server can be in a different Chef environment than the agents.