Fix the warning message of CINDER_MULTI_LVM_BACKEND

CINDER_MULTI_LVM_BACKEND is marked as deprecated and we recommend
to use CINDER_ENABLED_BACKENDS instead now. However current warning
message shows that CINDER_ENABLED_BACKENDS will be removed.
This patch fixes the message.

Change-Id: I3ca25e4273c3abebce1cfefe1ae4af622b71e993
diff --git a/stack.sh b/stack.sh
index 7bfd072..7aa2d05 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1456,7 +1456,7 @@
         echo_summary "WARNING: CINDER_MULTI_LVM_BACKEND is used"
         echo "You are using CINDER_MULTI_LVM_BACKEND to configure Cinder's multiple LVM backends"
         echo "Please convert that configuration in local.conf to use CINDER_ENABLED_BACKENDS."
-        echo "CINDER_ENABLED_BACKENDS will be removed early in the 'K' development cycle"
+        echo "CINDER_MULTI_LVM_BACKEND will be removed early in the 'K' development cycle"
         echo "
 [[local|localrc]]
 CINDER_ENABLED_BACKENDS=lvm:lvmdriver-1,lvm:lvmdriver-2