DSpace 6+ uses a UUID for item identifiers instead of an integer so
we need to adapt our tests accordingly. The Python UUID object must
be cast to a string to use it elsewhere in the code.
Falcon's response content is raw bytes, while its text is a string.
Let's use the latter so we can use json.loads() in Python 3.5, 3.6,
and 3.7 with the same code.
See: https://falcon.readthedocs.io/en/stable/api/testing.html