isolate: allow argument passing

garlic/stages/isolate/stage1

@@ -46,4 +46,4 @@ mounts=(
 join_flags="${mounts[@]}"
 
 exec $nixjoin -i $join_flags $nixhome -- \
-	env -i "${env[@]}" @out@/bin/stage2
+	env -i "${env[@]}" @out@/bin/stage2 "$@"

garlic/stages/isolate/stage2

@@ -13,4 +13,4 @@ if [ -e /usr ]; then
   exit 1
 fi
 
-exec @program@
+exec @program@ "$@"