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.

Bug-Url: https://bugzilla.redhat.com/1111234
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>
Reviewed-on: http://gerrit.ovirt.org/29725
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>