Fix VM race conditions #2787

Job	Run time
Code (oldstable)	4m 48s
Code (stable)	4m 28s
Code (tip)	7m 12s
System (stable, cluster, dir)	8m 25s
System (stable, cluster, btrfs)	8m 24s
Client (oldstable, ubuntu-latest)	1m 24s
System (stable, cluster, lvm)	8m 24s
Client (oldstable, macos-latest)	1m 30s
System (stable, cluster, zfs)	8m 23s
Client (oldstable, windows-latest)	1m 37s
System (stable, cluster, ceph)	8m 24s
System (stable, cluster, random)	8m 22s
Client (stable, ubuntu-latest)	1m 37s
System (stable, standalone, dir)	8m 22s
Client (stable, macos-latest)	1m 35s
System (stable, standalone, btrfs)	8m 23s
Client (stable, windows-latest)	1m 41s
System (stable, standalone, lvm)	8m 23s
System (stable, standalone, zfs)	8m 24s
Documentation	5m 10s
System (stable, standalone, ceph)	8m 24s
System (stable, standalone, random)	8m 24s
System (oldstable, cluster, dir)	8m 24s
System (oldstable, standalone, dir)	8m 26s
System (tip, cluster, dir)	8m 24s
System (tip, standalone, dir)	8m 29s
	2h 45m 27s

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