OData needs to account for source order and org.teiid.defaultNullOrder

Teiid's default null handling (low) matches that of the odata spec. However we don't have strict enforcement that pushdown order bys must match that ordering - only an option to do so if it's supported by the source org.teiid.pushdownDefaultOrderBy. We also have org.teiid.defaultNullOrder which can be set to something other than low. In either of those cases the returned ordering will not match the spec: http://docs.oasis-open.org/odata/odata/v4.01/cs01/part1-protocol/odata-v4.01-cs01-part1-protocol.html#_Toc505771210