testing: Fix systemctl wrapper and adapt enabling services on winnetou

testing: Fix systemctl wrapper and adapt enabling services on winnetou

The wrapper called the command twice for any unit but "strongswan" and
it didn't return the correct exit code.  This was noticed when an
if-updown script tried to check if systemd-resolved is active and always
succeeded, which caused failing attempts to configure it.

But now that the return code is correct, trying to enable bind9 won't
fail silently anymore if the unit doesn't exist (similar on older systems
for named), so this is adapted.