tls: accept empty `net.Socket`s

Accept `new net.Socket()` as a `socket` option to `tls.connect()`
without triggering an assertion error in C++.

This is done by wrapping it into a JSStream to ensure that there will be
a handle at the time of wrapping the socket into TLSSocket.

Fix: https://github.com/iojs/io.js/issues/987
PR-URL: https://github.com/iojs/io.js/pull/1046


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>