OAK-1027: Avoid turning multivalued properties to String arrays

Use Iterable<String> in the ImmutablePrivilegeDefinition constructor so we don't have to go through a String array or an extra Set instance

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1524803 13f79535-47bb-0310-9956-ffa450edef68