tls: fix tls handshake check in ssl error

In ssl.onerror event, `this` refers `ssl` so that
`this._secureEstablished` is always undefined. Fix it to refer
TLSSocket.

PR-URL: #1661
Reviewed-By: Fedor Indutny <fedor@indutny.com>

lib/_tls_wrap.js

@@ -362,7 +362,7 @@ TLSSocket.prototype._init = function(socket, wrap) {
     self._writableState.errorEmitted = true;
 
     // Destroy socket if error happened before handshake's finish
-    if (!this._secureEstablished) {
+    if (!self._secureEstablished) {
       self._tlsError(err);
       self.destroy();
     } else if (options.isServer &&