Add a deprecation warning for lib/neutron-legacy

This commit adds a deprecation warning for lib/neutron-legacy. Right
now lib/neutron isn't quite in a place where we can use it by default
but we're getting close. As soon as it's passing in the gate we plan
to make a switch over and a hard delete of lib/neutron-legacy. To give
any users which have a hard dependency on it (which is not actually
a supported use case) a heads up this adds the deprecation warning
in front of that change.

Change-Id: Idf1faf2e9dd497f9b97abfcc6e796ca72d60d955
diff --git a/lib/neutron-legacy b/lib/neutron-legacy
index 7eb8637..a3a0dcc 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -61,7 +61,7 @@
 # Neutron Network Configuration
 # -----------------------------
 
-
+deprecated "Using lib/neutron-legacy is deprecated, and it will be removed in the future"
 
 if is_ssl_enabled_service "neutron" || is_service_enabled tls-proxy; then
     Q_PROTOCOL="https"