'Login to an appliance using a user name and password.
Start a session like what is done logging into the BUI.  This is not a
requirement to run REST commands, since the protocol is stateless.
What is does is set up a cookie session so that some server side
caching can be done.  If login is used remember to call logout when
finished.
:param auth_str: Authorization string (base64)'

def login(self, auth_str):

    self.auth_str = auth_str
    self._authorize()
