RFR 8186186 : GSSContext.isEstablished() can return true on error state

[Ivan Gerasimov]

Hello!

Would you please help review the fix?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8186186
WEBREV: http://cr.openjdk.java.net/~igerasim/8186186/01/webrev/

With kind regards,
Ivan