Add unix:// prefix for socket addresses used by CRI remote client.

[Random-Liu]

Kubelet and crictl prefers socket address with unix:// prefix, or else it prints out warning. https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/util/util_unix.go#L75

For example:

# crictl ps
W0420 17:20:40.130286  237131 util_unix.go:75] Using "/run/containerd/containerd.sock" as endpoint is deprecated, please consider using full url format "unix:///run/containerd/containerd.sock".
CONTAINER ID        IMAGE               CREATED             STATE               NAME                ATTEMPT

This PR adds unix:// prefix to all containerd socket addresses except the ones passed to containerd client, because containerd client doesn't work with the unix:// prefix.

Signed-off-by: Lantao Liu [email protected]

[Random-Liu]

This PR also updates cri-tools to include the fix kubernetes-sigs/cri-tools#291

[Random-Liu]

/test pull-cri-containerd-build

[mikebrow]

/LGTM