Elytron - Write SASL mechanism implementing class into trace log

It's very hard to debug issues when a wrong SASL mechanism implementation is used (e.g. JDK provided one instead Elytron one). The class name implementing the mechanism should be logged by Elytron.

One place to cover this could be org.wildfly.security.auth.client.AuthenticationConfiguration.createSaslClient() method, but there are probably more places to look into.