tests: Use relative path for python3 compliance

Change-Id: I9a45a7800f1b69037781374df86e29bd5eb0f014
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26255
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

tests/testing/tests.py

@@ -39,7 +39,8 @@ from abc import ABCMeta, abstractmethod
 import os
 from collections import namedtuple
 from units import *
-from results import TestResult
+from .helpers import FileIgnoreList
+from .results import TestResult
 import shutil
 
 _test_base = os.path.join(os.path.dirname(__file__), "..")