unified pers: fix restoration when moving from ifcfg pers

Up until now we were only flushing the persistence of the
configurator currently set up. This had the problem that when
switching between configurators and persistence models, old
persistence remainders could be left over.

Bug-Url https://bugzilla.redhat.com/1064530
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Change-Id: I584b3b2ee953b508da23874c0adc79fe59e06856
Reviewed-on: http://gerrit.ovirt.org/25063
Tested-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>