Network functional tests assertion improvements

This change allows for more fine grained assertion errors. It allows
, among other things, to differentiate if what failed is making a
net or putting it into the running configuration.

Change-Id: Icca9a552272818039bc677c6adebfed3d5664454
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20123
Reviewed-by: Dan Kenigsberg <danken@redhat.com>