SLING-3768 - Be more resilient when .content.xml listing and filesystem
disagree on child nodes

Create an AddOrUpdateNodeCommandTest to verify basic scenarios of the
AddOrUpdateNodeCommand

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1612547 13f79535-47bb-0310-9956-ffa450edef68
SLING-3778 - [tooling] multi valued properties are not correctly
exported to the server

When a single-valued property must be updated to have multiple values,
remove it altogether and then set the values.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1612548 13f79535-47bb-0310-9956-ffa450edef68