json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

This test is unstable and prone to error, it's not clear if this is an actual issue with radosgw, a race condition, or something else.

```
2022-06-23 06:13:14 [INFO] Retrieving product stream information from https://172.16.0.87:443/swift/v1/simplestreams/data//streams/v1/auto.sync.json
2022-06-23 06:14:44 [INFO] ERROR
2022-06-23 06:14:44 [INFO] ======================================================================
2022-06-23 06:14:44 [INFO] ERROR: test_110_local_product_stream (zaza.openstack.charm_tests.glance_simplestreams_sync.tests.GlanceSimpleStreamsSyncTest)
2022-06-23 06:14:44 [INFO] Verify that the local product stream is accessible and has data.
2022-06-23 06:14:44 [INFO] ----------------------------------------------------------------------
2022-06-23 06:14:44 [INFO] Traceback (most recent call last):
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/zaza/openstack/charm_tests/glance_simplestreams_sync/tests.py", line 125, in test_110_local_product_stream
2022-06-23 06:14:44 [INFO] _check_local_product_streams(expected_images)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 324, in wrapped_f
2022-06-23 06:14:44 [INFO] return self(f, *args, **kw)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 404, in __call__
2022-06-23 06:14:44 [INFO] do = self.iter(retry_state=retry_state)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 349, in iter
2022-06-23 06:14:44 [INFO] return fut.result()
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/concurrent/futures/_base.py", line 437, in result
2022-06-23 06:14:44 [INFO] return self.__get_result()
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/concurrent/futures/_base.py", line 389, in __get_result
2022-06-23 06:14:44 [INFO] raise self._exception
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 407, in __call__
2022-06-23 06:14:44 [INFO] result = fn(*args, **kwargs)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/zaza/openstack/charm_tests/glance_simplestreams_sync/tests.py", line 118, in _check_local_product_streams
2022-06-23 06:14:44 [INFO] product_streams = get_product_streams(url)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 324, in wrapped_f
2022-06-23 06:14:44 [INFO] return self(f, *args, **kw)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 404, in __call__
2022-06-23 06:14:44 [INFO] do = self.iter(retry_state=retry_state)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 360, in iter
2022-06-23 06:14:44 [INFO] raise retry_exc.reraise()
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 193, in reraise
2022-06-23 06:14:44 [INFO] raise self.last_attempt.result()
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/concurrent/futures/_base.py", line 437, in result
2022-06-23 06:14:44 [INFO] return self.__get_result()
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/concurrent/futures/_base.py", line 389, in __get_result
2022-06-23 06:14:44 [INFO] raise self._exception
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/tenacity/__init__.py", line 407, in __call__
2022-06-23 06:14:44 [INFO] result = fn(*args, **kwargs)
2022-06-23 06:14:44 [INFO] File "/home/ubuntu/src/review.opendev.org/openstack/charm-glance-simplestreams-sync/.tox/func-target/lib/python3.8/site-packages/zaza/openstack/charm_tests/glance_simplestreams_sync/tests.py", line 46, in get_product_streams
2022-06-23 06:14:44 [INFO] return json.loads(json_data)
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/json/__init__.py", line 357, in loads
2022-06-23 06:14:44 [INFO] return _default_decoder.decode(s)
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/json/decoder.py", line 337, in decode
2022-06-23 06:14:44 [INFO] obj, end = self.raw_decode(s, idx=_w(s, 0).end())
2022-06-23 06:14:44 [INFO] File "/usr/lib/python3.8/json/decoder.py", line 355, in raw_decode
2022-06-23 06:14:44 [INFO] raise JSONDecodeError("Expecting value", s, err.value) from None
2022-06-23 06:14:44 [INFO] json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
2022-06-23 06:14:44 [INFO] ----------------------------------------------------------------------
```

ci job results: https://openstack-ci-reports.ubuntu.com/artifacts/7ea/847251/1/check/focal-wallaby/7ea9c01/
patch: https://review.opendev.org/c/openstack/charm-glance-simplestreams-sync/+/847251