relayd: track worker thread's epoll fd using the fd-tracker

relayd: track worker thread's epoll fd using the fd-tracker

This commit introduces an fd leak report (bogus) which is caused
by another thread using the same poll initialization functions as
the worker thread.

The fd is cleaned-up by that other thread, but the fd-tracker
is not aware of this, thus causing the report.

This is adressed in a follow-up patch.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I105fddcf3421373f9746c1d8f31016462af2448e