connectivty log: more readable changes

Before this patch, the name of a new interface, as well as the name of
an interface with a changed property, was not recorded in
/var/log/connectivity.log. This patch add an <iface_name>: qualifier to
make the log more informative.

Change-Id: Ib918b30a2bbf766495010424c5e149cee9768020
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29654
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>