virt: Ensure not to handle no longer tracked fds in epoll

In some cases it is possible that events from epoll are received before the
socket is closed. This patch ensures that we're ignoring events which belong
to fds we are not tracking (anymore).

Change-Id: Idde0f89d2859107dd1bb697d1753709137335677
Bug-Url: https://bugzilla.redhat.com/1102072
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28179
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Gal Hammer <ghammer%redhat.com@gtempaccount.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>