backport v2021pre ← v2022dev0: lava: There's no connmand-wait-online on NFS

Backport of !225 (merged)

The NFS rootfs does not ship connmand-wait-online, so at the moment this only produces an error message as the error is ignored:

ash: connmand-wait-online: not found

See https://lava.collabora.co.uk/scheduler/job/2869103#L1082