Trusted and latest root metadata are expired

[phenaproxima]

Description: This should be a simple fixture with server- and client-side metadata. The root metadata in both directories should have a date way in the past, to guarantee that it is expired and cannot be updated. The server-side metadata should have an additional version, in which the root metadata should have an expiration date that is later than the previous version, but still expired.

Procedure: TBD; I'm not clear yet on how to manually modify the expiration date of any given piece of metadata, beyond forcibly re-signing it. We will likely need to publish the fixture twice (once with the client, once without) in order to create a new version of the server-side metadata.

Expected Outcome: The TUF client should fail because the most recent available root metadata is expired.