tests/functional: Convert some tests that download files via fetch_asset()

Now that we've got the Asset class with pre-caching, we can convert
some Avocado tests that use fetch_asset() for downloading their
required files.

Message-ID: <20240830133841.142644-18-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
11 files changed