Authentication errors cause #node_name to return nil

[capoferro]

https://github.com/RiotGames/motherbrain/blob/master/lib/mb/node_querier.rb#L93

This should catch authentication errors and notify the user that the node is not reachable due to failed authentication rather than just returning nil, making the caller think the node does not have a node_name.

In broader strokes, this error handling should be much more fine grained rather than just being a catch all.

This behavior was observed when communicating with windows nodes over winrm. Unsure if this occurs over ssh as well.