[9] RFR: 8129389: javax/net/ssl/DTLS tests fail intermittently

[Artem Smotrakov]

Hello,

Please review the following patch for DTLS tests.

A couple of DTLS tests which are based on DTLSOverDatagram.java fail 
intermittently. I was not able to reproduce these failures. I am 
proposing to update the tests to print more information to logs, so that 
more information will be available if they fail next time.

I also noticed that the tests doesn't check for FINISHED handshake 
status which can be returned by wrap/unwrap methods. This status should 
indicate that handshake finished.

Changes:
- enabled debug output by setting "javax.net.debug" system property to "ssl"
- added more logging to handshaking code
- updated handshaking code to check for FINISHED status
- added more checks to handshaking code
- added try-with-resources blocks for sockets and file input streams
- removed suppressed exceptions to make logs clearer

Bug: https://bugs.openjdk.java.net/browse/JDK-8129389
Webrev: http://cr.openjdk.java.net/~asmotrak/8129389/webrev.00/

Artem