GSSAPI compatibility tests and fixes

Tests of binary compatibility Elytron GSSAPI implementation + fixes of founded deviations.

I am not sure about getWrapSizeLimit() moving - Darran, can you check if this not harm something? (meaning of `actualMaxReceiveBuffer` was changed from max nonwrapped size to max wrapped size and `maxBuffer` oppositely)

I hope change `JAASUtil` and `TestKDC` to public (because using it in subpackage) in test scope will not be a problem.

* Fixed AbstractGssapiMechanism.DEFAULT_MAX_BUFFER_SIZE (3 octets =
0xFFFFFF)
* Fixed bugs in networkOrderBytesToInt() and intToNetworkOrderBytes()
~~(and changed to static and package private to allow direct testing)~~
* ChallengeResponseState should return byte[0] instead of null
* SecurityLayerAdvertiser: gssContext.getWrapSizeLimit() moved on the
opposite side of communication
* getNegotiatedProperty now returns Strings