Fix Bug: Timezone is ignored, always same as host

Bug affects normal interactive usage (example/guided.py).

The timezone configured in the installer is not the timezone that
ends up in the new installed system. Instead, the timezone
used in the host system (from where the installer is run) is the
one that finally ends up being used.

Reason: systemd-nspawn by default copies the host timezone into
the target. And systemd-nspawn is run when keyboard-layout is
changed (which is done after changing the timezone).

Solution: Add option `--timezone=off` to systemd-nspawn, which
hinders affecting the timezone in the target.

archinstall/lib/systemd.py

@@ -64,6 +64,7 @@ class Boot:
 			self.session = SysCommandWorker([
 				'/usr/bin/systemd-nspawn',
 				'-D', self.instance.target,
+				'--timezone=off',
 				'-b',
 				'--machine', self.container_name
 			])