title: When and why to use load_host_keys and load_system_host_keys?
body: <p>I am connecting to a host for the first time using its private key file. Do I need to call load_host_keys function before connecting to the host? Or Can I just skip it? I have the autoAddPolicy for missing host key but how can python know the location of the host key file?</p>
  
  <p>Hence my question, when to use the function load_host_key?</p>