In python client, upload on non existing container automatically creates the container contrary to what is statded in the documentation

[Romain]

- [x] This doc is inaccurate in this way:

In upload documentation:
`If the given container or account does not exist, the upload method will raise a SwiftError, otherwise an iterator over the results generated for each object upload is returned.`

However, container is created when calling upload with non-existing container. (tested in 3.12)

-----------------------------------
Release: 3.12.1.dev1 on 2019-03-25 09:35:47
SHA: 8bd346f3b9abda7282fffb6bbe7341577ca1dff1
Source: https://opendev.org/openstack/python-swiftclient/src/doc/source/service-api.rst
URL: https://docs.openstack.org/python-swiftclient/xena/service-api.html