Fix timedatectl parsing for newer systemd releases

**This will likely have a merge conflict with #12724.  If that PR is merged first, ping me and I'll rebase and fix this one.**

systemd 210 changed the output for timedatectl, changing 'Timezone' to
'Time zone'. This commit fixes a traceback that occurs in
timezone.get_zone for these newer versions of systemd.

Additionally, for get_zone() and get_hwclock(), parsing of timedatectl
has been changed from an ugly and unwieldy shell one-liner to actual
python logic.

Finally, output_loglevel has been set to 'debug' for all shell commands
in this module, part of a greater effort to make the logs less noisy.