add lvm-on-luks partition to crypttab

[beerriot]

I was trying to restore a snapshot from one Linux Mint installation onto a fresh install. Timeshift would transfer all files, but the restored installation would be unbootable. The boot would hang at the Mint splash screen with a message about how it was waiting for something to provide a particular partition UUID.

The UUID it was waiting for was the LUKS partition on my original installation. Timeshift hadn't updated /etc/crypttab with the UUID of my new LUKS partition.

I tracked this down to the fact that the way the Linux Mint installer sets up encryption is LVM-on-LUKS. The LVM layer between LUKS and ext4 caused Device.is_on_encrypted_partition() to return false when called for my root mount point.

These are the relevant lines of the lsblk output that Timeshift used to determine my device layout:

NAME="sda3" KNAME="sda3" LABEL="" UUID="65b13e9a-6d8f-4171-a265-db88f13a4c75" TYPE="part" FSTYPE="crypto_LUKS" SIZE="497947770880" MOUNTPOINT="" MODEL="" RO="0" HOTPLUG="0" MAJ:MIN="8:3" PARTLABEL="" PARTUUID="39b0cf2e-601a-4cd3-a2d8-96aaa433d662" PKNAME="sda" VENDOR="" SERIAL="" REV=""
NAME="luks-65b13e9a-6d8f-4171-a265-db88f13a4c75" KNAME="dm-0" LABEL="" UUID="DoB34I-5txT-3nlV-548q-B0Wz-Ox9m-NBt0YG" TYPE="crypt" FSTYPE="LVM2_member" SIZE="497930993664" MOUNTPOINT="" MODEL="" RO="0" HOTPLUG="0" MAJ:MIN="252:0" PARTLABEL="" PARTUUID="" PKNAME="sda3" VENDOR="" SERIAL="" REV=""
NAME="vgmint-root" KNAME="dm-1" LABEL="" UUID="6e019126-e3fd-43d1-af5c-8d3eada27ab7" TYPE="lvm" FSTYPE="ext4" SIZE="495850618880" MOUNTPOINT="/" MODEL="" RO="0" HOTPLUG="0" MAJ:MIN="252:1" PARTLABEL="" PARTUUID="" PKNAME="dm-0" VENDOR="" SERIAL="" REV=""

Device.is_on_encrypted_partition is looking for TYPE to be crypt, but for mine it is lvm. It's the parent of that partition that has type crypt. That's because it's the grand-parent that is the LUKS partition.

I added the grand-parent check, and then Timeshift correctly updated my /etc/crypttab.

I think this change may address the problem noted in #302.