Some service APIs such as Swift list public containers does not require
a token. Therefore, there will be no identity or service catalog information
available. In these cases, audit should fill in the default
(i.e. taxonomy.UNKNOWN) for both initiator and target instead of raising an
exception.
Change-Id: I3f3c12d5e8c0fa176fb7f0218c368971e0a9d0b5
Closes-Bug: 1583699