Incorrect key hash encoding for XCDRv2 writer

[dpotman]

In Cyclone's C++ binding, the key hash for an XCDRv2 writer is serialized as basic CDR (optionally md5-hashed), which is incorrect; the key hash encoding format should follow the encoding that is used for writing the sample (see also XTypes specification section 7.6.8, although there is some unclarity, see https://issues.omg.org/issues/DDSXTY14-11).

Although Cyclone does not use key hashes, and the key hash is not included unless explicitly enabled, enabling this feature could potentially break interoperability with other DDS implementations that expect XCDR2 key hash encoding.