sys handler needs to exclude raid and lvm partitions from sfdisk

On Debian 9 Stretch, sfdisk gives warnings when you try to backup the partition tables for a device that doesn't have any, such as raid or lvm partitions.

I have fixed this on my own system by excluding those files in the device gathering stage on line 610 https://0xacab.org/riseuplabs/backupninja/blob/master/handlers/sys.in#L610

devices=`LC_ALL=C $SFDISK -l 2>/dev/null | grep "^Disk /dev" | grep -v mapper | grep -v md| /usr/bin/awk '{print $2}' | cut -d: -f1`