Connects to the Responsys soap service

        Uses the credentials passed to the client init to login and setup the session id returned.
        Returns True on successful connection, otherwise False.

def connect(self):
        """ Connects to the Responsys soap service

        Uses the credentials passed to the client init to login and setup the session id returned.
        Returns True on successful connection, otherwise False.
        """

        if self.session and self.session.is_expired:
            # Close the session to avoid max concurrent session errors
            self.disconnect(abandon_session=True)

        if not self.session:

            try:
                login_result = self.login(self.username, self.password)
            except AccountFault:
                log.error('Login failed, invalid username or password')
                raise
            else:
                self.session = login_result.session_id

        self.connected = time()
        return self.connected