Checks if the device is in configuration mode or not.

        IOS-XR, unfortunately, does this:
        RP/0/RSP0/CPU0:BNG(admin)#

def check_config_mode(self, check_string=")#", pattern=r"[#\$]"):
        """Checks if the device is in configuration mode or not.

        IOS-XR, unfortunately, does this:
        RP/0/RSP0/CPU0:BNG(admin)#
        """
        self.write_channel(self.RETURN)
        output = self.read_until_pattern(pattern=pattern)
        # Strip out (admin) so we don't get a false positive with (admin)#
        # (admin-config)# would still match.
        output = output.replace("(admin)", "")
        return check_string in output