incus: Handle non-existent home directory #378

Job	Run time
Documentation	6m 39s
Client (1.20.x, ubuntu-latest)	29s
System (1.20.x, cluster, dir)	11m 18s
Code	7m 1s
Client (1.20.x, macos-latest)	1m 20s
System (1.20.x, cluster, btrfs)	12m 41s
System (1.20.x, cluster, lvm)	12m 16s
System (1.20.x, cluster, zfs)	12m 20s
Client (1.20.x, windows-latest)	2m 10s
System (1.20.x, cluster, ceph)	15m 38s
System (1.20.x, cluster, random)	11m 19s
System (1.20.x, standalone, dir)	21m 44s
System (1.20.x, standalone, btrfs)	21m 43s
System (1.20.x, standalone, lvm)	41m 6s
System (1.20.x, standalone, zfs)	42m 47s
System (1.20.x, standalone, ceph)	1h 15m 28s
System (1.20.x, standalone, random)	22m 15s
System (stable, cluster, dir)	12m 16s
System (stable, standalone, dir)	22m 21s
System (tip, cluster, dir)	12m 31s
System (tip, standalone, dir)	22m 41s
	6h 28m 3s

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