lxd-to-incus: Handle mountpoints #474

Job	Run time
Code tests	9m 8s
Client tests (1.20.x, ubuntu-latest)	36s
Client tests (1.20.x, macos-latest)	46s
Documentation tests	12m 26s
Client tests (1.20.x, windows-latest)	1m 57s
System tests (1.20.x, cluster, dir)	13m 11s
System tests (1.20.x, cluster, btrfs)	16m 48s
System tests (1.20.x, cluster, lvm)	14m 42s
System tests (1.20.x, cluster, zfs)	17m 10s
System tests (1.20.x, cluster, ceph)	17m 32s
System tests (1.20.x, cluster, random)	17m 32s
System tests (1.20.x, standalone, dir)	23m 22s
System tests (1.20.x, standalone, btrfs)	25m 6s
System tests (1.20.x, standalone, lvm)	40m 36s
System tests (1.20.x, standalone, zfs)	41m 59s
System tests (1.20.x, standalone, ceph)	1h 20m 21s
System tests (1.20.x, standalone, random)	37m 2s
System tests (stable, cluster, dir)	13m 31s
System tests (stable, standalone, dir)	20m 21s
System tests (tip, cluster, dir)	13m 16s
System tests (tip, standalone, dir)	24m 34s
	7h 21m 56s

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