Make sure to notify handshake success even if SSLEngine is closed

Related:

e9685ea45aebcb4f9dad0f3a1fc328a06b4932dd

Motivation:

SslHandler.unwrap() does not evaluate the handshake status of
SSLEngine.unwrap() when the status of SSLEngine.unwrap() is CLOSED.

It is not correct because the status does not reflect the state of the
handshake currently in progress, accoding to the API documentation of
SSLEngineResult.Status.

Also, sslCloseFuture can be notified earlier than handshake notification
because we call sslCloseFuture.trySuccess() before evaluating handshake
status.

Modifications:

- Notify sslCloseFuture after the unwrap loop is finished
- Add more assertions to SocketSslEchoTest

Result:

Potentially fix the regression caused by:
- e9685ea45aebcb4f9dad0f3a1fc328a06b4932dd
Add log messages when dump starts

.. to make it easier to find the right dump file for a test when there
are multiple dump files.