Bug#947807: systemd: can't install systemd when /etc/machine-id is a symbolic link to /dev/null

[Joshua Hudson]

# apt-get install systemd-sysv
[lots of junk]
Initializing machine ID from random generator.
Failed to truncate /etc/machine-id: Invalid argument

This is trivially verified by

# dpkg-reconfigure systemd
Initializing machine ID from random generator.
Failed to truncate /etc/machine-id: Invalid argument
#