refactoring: Configurator base class making attributes explicit.

Currently the base class contains references to internal attributes
in some methods that are instantiated in the subclass Ifcfg.
Proposed refactoring let the baseclass instantiate the configApplier
and the _libvirtAdded set.

Change-Id: I6e5719146493c83349d18284fa1f67f99bc239fa
Signed-off-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/16845
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>