ipwrapper: do not report devices that disappear

There was a race in getLinks that consisted on devices disappearing
between them being reported by netlink and information being
retrieved by the Link class (driver info).

This patch solves it by reporting just those links that suceed.

Change-Id: Ib41336f3ac2f2278db2706f7d4eb3a9b579f66d4
Bug-Url: https://bugzilla.redhat.com/1129377
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29442
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29546
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31419
Tested-by: Dan Kenigsberg <danken@redhat.com>