libvirt_configure: unpersist logrotate.d/libvirt

On commit 247a76e7 we moved the libvirt settings to libvirt_configure.sh.in and now
we see that vdsm cannot rename temp. file to /etc/logrotate.d/libvirtd on
ovirt-node system at the stage we execute vdsm-tool configure --force.
This patch will add the command unpersist before renaming the file,
otherwise ovirt-node will complain with "Device or resource busy".

Change-Id: Icd0e6b3ea39680ac3fc8ec5731aa6be3bd8e4deb
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1074257
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/25700
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>