libvirt_configure: move unpersist up

On commit b4efa0036e065 we have fixed the failure on
mv command to logrotate file but a few lines above vdsm
executes a sed which also requires the file be unpersist before it.
This patch move the unpersist command some lines above.

Change-Id: Iea6ae62990a414f52225ad690ec9c21060c2a48d
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/25990
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>