feat(tmpfiles) add some more /etc symlinks

Support was added for the following symlinks:
  /etc/os-release  -> /usr/share/coreos/os-release
  /etc/lsb-release -> /usr/share/coreos/lsb-release

Other packages create these files, but if they get removed from the
system, they will be properly re-created now by the systemd-tmpfiles
program.