Guacamole now uses local hostnames

[gmiranda23]

• Guacamole was hitting incorrect hostname (going to external IP from the portal node) for ssh/rdp.
• When corrected, it became clear that credentials needed to be managed for different nodes.
• Guacamole creds now stored in node attributes. Lookup LWRP modified to manage guacamole attributes.
• Realized we need private key for ssh of unmanaged nodes and eventual admin password resolution (see #19).
• In managing keys, discovered bug where provisioning was creating a chef_default key due to unspecified machine_options.
• Added private key auth for unmanged nodes (and a throwaway private key in the repo, ugh. to be fixed by #37).

Guacamole now works for all Linux nodes (workstation prompts for password)

Resolves #21