tests: fix name collisions in verifier.py

tests: fix name collisions in verifier.py

In verifier.py, testlib.test_util is imported and renamed to 'test',
while several functions in the file have a subfunction named 'test()',
which causes test.fail() to fail as 'test' points to the
subfunction instead of the module.

This commit addresses the above issue by keeping the imported module
as test_util instead of renaming it to test.

Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Change-Id: I0ab7b52619f2fa9495e9a6ff8d469c022eea98bc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31994
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>