sourcerouting: make thread daemonic

The Python interpreter waits for non daemonic threads. The
sourceRouteThread shouldn't keep the process waiting.

Change-Id: I45effe0d787c36564a1ae3eb45844c22ac2a2c36
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/22345
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Assaf Muller <amuller@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>