fix: change spread stdout style to header by default

tools/spread.sh

@@ -54,8 +54,8 @@ _ssh() {
 
 for server in $SPREAD_SERVERS; do
     # while loop so we get:: $SPEAD_USER@$server: <output>
-    case ${SPREAD_LOG_STYLE:-prefixed} in
-        prefixed)
+    case ${SPREAD_LOG_STYLE:-header} in
+        prefix|prefixed)
             _ssh $server | while read -r line; do
                 printf "%s@%-10s: %s\n" "$SPREAD_USER" "$server" "$line"
             done