crypto: honor default ciphers in client mode

Right now no default ciphers are use in, e.g. https.get, meaning that
weak export ciphers like TLS_RSA_EXPORT_WITH_DES40_CBC_SHA are accepted.

To reproduce:

node -e "require('https').get({hostname: 'www.howsmyssl.com', \
  path: '/a/check'}, function(res) {res.on('data', \
  function(d) {process.stdout.write(d)})})"