refactor(templates): replace "! -z" with "-n" for better readability

jvb/rootfs/etc/cont-init.d/10-config

@@ -16,7 +16,7 @@ fi
 
 # Migration from DOCKER_HOST_ADDRESS to JVB_ADVERTISE_IPS
 if [[ -z "${JVB_ADVERTISE_IPS}" ]]; then
-    if [[ ! -z "${DOCKER_HOST_ADDRESS}" ]]; then
+    if [[ -n "${DOCKER_HOST_ADDRESS}" ]]; then
         echo "WARNING: DOCKER_HOST_ADDRESS is deprecated, migrate to JVB_ADVERTISE_IPS"
         export JVB_ADVERTISE_IPS=${DOCKER_HOST_ADDRESS}
     fi