[Tables] User agent default fails only on Python2.7 with Cosmos account

[seankane-msft]

Issue tracking to tackle in next non-MQ epic. Issue is likely due to deserialization of the HTTP response, possibly a wrong User-Agent for cosmos vs. tables.

self = <azure.data.tables._models.TablePropertiesPaged object at 0x0000000005AF0788>
get_next_return = ('primary', None, {'Date': datetime.datetime(2020, 12, 2, 19, 17, 17, tzinfo=<FixedOffset 0.0>), 'x-ms-client-request-id': None, 'x-ms-continuation-NextTableName': None, 'x-ms-request-id': 'fe29c961-34d2-11eb-91f6-00155d000471', ...})

    def _extract_data_cb(self, get_next_return):
        self.location_mode, self._response, self._headers = get_next_return
>       props_list = [TableItem._from_generated(t, **self._headers) for t in self._response.value] # pylint:disable=protected-access
E       AttributeError: 'NoneType' object has no attribute 'value'

[ghost]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @southpolesteve, @zfoster