SLING-3979 - [tooling] multi valued properties are still not correctly
exported to the server

If a property is marked explicitly as multi-value, preserve that
information even if it only has one value.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1628832 13f79535-47bb-0310-9956-ffa450edef68