tests: use bytes and %d formatting in test-remotefilelog-datapack.py

Authored by indygreg.

Description

tests: use bytes and %d formatting in test-remotefilelog-datapack.py

There were numerous failures on Python 3 due to str/bytes mismatch
and '%s' not working for ints.

Differential Revision: https://phab.mercurial-scm.org/D5756