Remove the credentials from the resource model

Tying a username to a node in the resource is counter-intuitive when you have multiple service accounts on a machine.

For example. Let's say you have a "service" user and a "power" user that have specific privileges granted to them via sudoers. In the current model, you need two node definitions with duplicate information, one for power and another for service. The metadata about the node doesn't change, just the users associated with that "node." The only way to access this node is to filter on user.

Instead, the user should be able to choose from a list of credentials, both global and local to the logged in user. These credentials obey the rules of authorization. They are provided to the underlying dispatching command to authenticate the remote connection.