[9] RFR 8165275: Replace the reflective call to the implUpdate method in HandshakeMessage::digestKey

[Valerie Peng]

Hi Xuelei,

Could you please help reviewing this JSSE-related code refactoring?

Bug: https://bugs.openjdk.java.net/browse/JDK-8165275
Webrev: http://cr.openjdk.java.net/~valeriep/8165275/webrev.00/

Thanks,
Valerie