tests: Update memory tests to be compatible with python3

Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Change-Id: I9bb7444c62e6b29e9c91dbf30320a38718f08b8c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29353


Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>