vsudd: add /pkg/vsudd with README and example yml

Signed-off-by: Magnus Skjegstad <magnus@skjegstad.com>

pkg/vsudd/Dockerfile

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+FROM linuxkit/alpine:630ee558e4869672fae230c78364e367b8ea67a9 AS mirror
+
+RUN apk add --no-cache go musl-dev git build-base
+ENV GOPATH=/go PATH=$PATH:/go/bin 
+ENV VIRTSOCK_COMMIT=a381dcc5bcddf1d7f449495c373dbf70f8e501c0
+
+RUN git clone https://github.com/linuxkit/virtsock.git /go/src/github.com/linuxkit/virtsock && \
+    cd /go/src/github.com/linuxkit/virtsock && \
+    git checkout $VIRTSOCK_COMMIT && \
+    make vsudd
+
+FROM scratch
+COPY --from=mirror /go/src/github.com/linuxkit/virtsock/build/vsudd.linux /vsudd
+ENTRYPOINT ["/vsudd"]

pkg/vsudd/Makefile

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+default: push
+
+ORG?=linuxkit
+IMAGE=vsudd
+DEPS=$(wildcard *.go) Makefile Dockerfile
+
+HASH?=$(shell git ls-tree HEAD -- ../$(notdir $(CURDIR)) | awk '{print $$3}')
+
+tag: $(DEPS)
+	docker build --squash --no-cache -t $(ORG)/$(IMAGE):$(HASH) .
+
+push: tag
+	DOCKER_CONTENT_TRUST=1 docker pull $(ORG)/$(IMAGE):$(HASH) || \
+	DOCKER_CONTENT_TRUST=1 docker push $(ORG)/$(IMAGE):$(HASH)
+

pkg/vsudd/README.md

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+#### Vsudd
+
+Vsudd is a daemon that forwards unix domain socket traffic from the host to the
+guest VM via VSOCK. It can be used to control other daemons, like `containerd`
+and `dockerd`, from the host.  An example configuration file is available in
+[examples/vsudd.yml](/examples/vsudd.yml).
+
+After building the example, run the example with `linuxkit run hyperkit
+-vsock-ports 2374 vsudd`. This will create a unix domain socket in the state
+directory that map to the `containerd` control socket. The socket is called
+`guest.00000946`.
+
+If you install the `ctr` tool on the host you should be able to access the
+`containerd` running in the VM:
+
+```
+$ go get -u -ldflags -s github.com/containerd/containerd/cmd/ctr
+...
+$ ctr -a vsudd-state/guest.00000946 list
+ID        IMAGE     PID       STATUS
+vsudd               466       RUNNING
+```
+