Add compatibility for Python 3.6

src/mpsd_software_manager/__init__.py

src/mpsd_software_manager/cmds/available.py

src/mpsd_software_manager/cmds/install.py

src/mpsd_software_manager/cmds/prepare.py

src/mpsd_software_manager/cmds/status.py

src/mpsd_software_manager/mpsd_software.py

src/mpsd_software_manager/utils/filesystem_utils.py

src/mpsd_software_manager/utils/logging.py

src/mpsd_software_manager/utils/microarch.py

src/mpsd_software_manager/utils/run.py

tests/test_install.py

tests/test_logging.py

tests/test_prepare.py