Add check for size in CreatePersistentImg.sh (#1384)

INSTALL/CreatePersistentImg.sh

@@ -56,8 +56,13 @@ fi
 
 # check size
 if echo $size | grep -q "^[0-9][0-9]*$"; then
-    if [ $size -le 1 ]; then
-        echo "Invalid size $size"
+    vtMinSize=1
+    if echo $fstype | grep -q '^xfs$'; then
+        vtMinSize=16
+    fi
+    
+    if [ $size -lt $vtMinSize ]; then
+        echo "size too small ($size)"
         exit 1
     fi    
 else