'Connect to an SSH server.
Run a command remotely and return a file-like object for interaction
with the remote command.
:param host: Host name
:param command: Command to run (as argv array)
:param username: Optional ame of user to log in as
:param port: Optional SSH port to use'

def run_command(self, host, command, username=None, port=None):

    raise NotImplementedError(self.run_command)
