fsadm: avoid hidden --yes

When 'fsadm' was running without terminal (i.e. pipe), it's been
automatically working like in '--yes'.

Detect terminal and only accept empty "" input in this mode.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.172 - 
 ===============================
+  Stop using '--yes' mode when fsadm runs without terminal.
   Extend validation of filesystems resized by fsadm.
   Enhance lvconvert automatic settings of possible (raid) LV types.
   Allow lvchange to change properties on a thin pool data sub LV.

scripts/fsadm.sh

@@ -401,10 +401,15 @@ yes_no() {
 
 	while read -r -s -n 1 ANS ; do
 		case "$ANS" in
-		 "y" | "Y" | "") echo y ; return 0 ;;
-		 "n" | "N") echo n ; return 1 ;;
+		 "y" | "Y" ) echo y ; return 0 ;;
+		 "" ) if [ -t 1 ] ; then
+			echo y ; return 0
+		      fi ;;
 		esac
 	done
+
+	echo n
+	return 1
 }
 
 try_umount() {