RFR CSR for 8200400 Restrict Sasl mechanisms

[Weijun Wang]

Please review the CSR at

   https://bugs.openjdk.java.net/browse/JDK-8214331

One concern:

When a disabled mechanism is requested, Sasl.createClient and Sasl.createServer 
might silently return null and if a user has already taken for granted that a 
client should be returned an NPE will thrown somewhere. This is not quite 
friendly.

Thanks
Max