net: unref timer in parent sockets

`TLSSocket` wraps the original `net.Socket`, but writes/reads to/from
`TLSSocket` do not touch the timers of original `net.Socket`.

Introduce `socket._parent` property, and iterate through all parents
to unref timers and prevent timeout event on original `net.Socket`.

Fix: https://github.com/joyent/node/issues/9242
PR-URL: https://github.com/iojs/io.js/pull/891


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>