[REM3-29] Add support for the GSSAPI SASL mechanism to enable Kerberos authentication.

The core changes to Remoting were relatively small to enable the mechanism.

In addition a new test case is added based on work undertaken by Josef Cacek within the AS7 testsuite to bring in an embedded directory server and KDC to test GSSAPI/Kerberos authentication within the testsuite.

Unfortunately the test changes do bring in a number of additional dependencies, however Kerberos authentication is very sensitive so having the tests will quickly identify if any subsequent changes breaks it.