Acceptance Tests: bump Avocado version requirement to 85.0

This version (and 84.0) contain improvements that address specific
QEMU use cases, including:

 * Being able to download and use Fedora 31 images and thus
   re-activate the "boot_linux.py" tests

 * Being able to register local assets via "avocado assets register"
   and use them in tests

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20210211232835.2608059-2-crosa@redhat.com>
Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>

tests/requirements.txt

@@ -1,5 +1,5 @@
 # Add Python module requirements, one per line, to be installed
 # in the tests/venv Python virtual environment. For more info,
 # refer to: https://pip.pypa.io/en/stable/user_guide/#id1
-avocado-framework==83.0
+avocado-framework==85.0
 pycdlib==1.11.0