cleanup_image: hide messages from rpmdb rebuild

If version mismatch, rpm --rebuilddb will complain about some files, but is
isn't critical, so just hide those messages. We still take care of exit code.

cleanup_image

@@ -22,7 +22,7 @@ yum -c $PWD/yum.conf clean packages --installroot=$INSTALLDIR
 
 # Make sure that rpm database has right format (for rpm version in template, not host)
 echo "--> Rebuilding rpm database..."
-chroot `pwd`/mnt /bin/rpm --rebuilddb
+chroot `pwd`/mnt /bin/rpm --rebuilddb 2> /dev/null
 
 echo "--> Compacting image file..."
 dd if=/dev/zero of=mnt/fillme bs=1M 2> /dev/null || true