Invert logic to detect clab 0.75

docker/files/init-container.sh

@@ -22,7 +22,7 @@ sed -i -e 's,^root:.*,root:$y$j9T$kG8pyZEVmwLXEtXekQCRK.$9iJxq/bEx5buni1hrC8Vmvk
 /etc/init.d/ssh start
 
 # TODO(pim): Remove this after containerlab 0.75 is released
-if [ -r /etc/vpp/startup.conf ]; then
+if [ ! -r /config/vpp/startup.conf ]; then
   echo "Detected old containerlab binary - invoking backwards compatible behavior"
   STARTUP_CONFIG="/etc/vpp/startup.conf"
   VPPCFG_YAML_FILE="/etc/vpp/vppcfg.yaml"