Empty or invalid `.../containerd/daemon/io.containerd.grpc.v1.introspection/uuid` file created occasionally

[lmbarros]

In some rare cases, the /mnt/data/docker/containerd/daemon/io.containerd.grpc.v1.introspection/uuid created by containerd is empty (instead of containing an UUID). This causes some containerd operations to fail. Notably, the following command (which happens to be part of the current balenaEngine health check)

# balena-engine-containerd-ctr --address "/run/balena-engine/containerd/balena-engine-containerd.sock" version

will fail with

invalid UUID length: 0: unknown