Fix a typo in a var name in ChangePassword task

This has an affect on fedora and ubuntu instances, where user password
is not changed. Only the root one.

snf-image-helper/tasks/50ChangePassword.in

@@ -40,8 +40,8 @@ linux_password() {
 
     local distro=$(get_distro $target)
 
-    if [ "x$disto" = "xubuntu" -o \
-         "x$disto" = "xfedora" ] ; then
+    if [ "x$distro" = "xubuntu" -o \
+         "x$distro" = "xfedora" ] ; then
         users+=("user")
     fi