Backport : Not all properties of an hst:mount are exposed

An hst:mount can have an unlimited number of properties (node properties) since it is relaxed, but a developer cannot get a list of all of them. There's simply no API method to list all available properties of an hst:mount.

Method getAllProperties() seemed that it would do the trick, but it only returns those properties whose name starts with "hst:mount"

Also, JCR API is not applicable, since the liveuser used by HST doesn't have permission to access an hst:mount node.