Password Handling

Put the list of passwords needed by components into the component definition in the YAML file so the main program can ask for them (and populate a cache) before invoking any component classes. Change the password generator to have 2 methods, discover_password(name, prompt) and get_password(name). discover_password() will ask the user or generate a value, but get_password() only does a lookup of known values. The main program should use discover_password() in a loop. The components should all just use get_password().