Fixed Packet.shouldUseMtomOutbound to take into account a pre-existing content type that might have been set by a prior decode of an outbound Packet
Also added check in MtomCodec to prevent MTOM message with null content id and boundary from being generated, although after the above fix, this case is not expected to happen
Merge branch 'desagar_bug_17968180' of /private/git/repositories/fmw-infra-metro/jaxws-ri