Move mount back to its own package, not inside docker

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

pkg/mount/Dockerfile

@@ -0,0 +1,11 @@
+FROM alpine:3.5
+
+RUN \
+  apk update && apk upgrade -a && \
+  apk add --no-cache \
+  jq \
+  sfdisk \
+  && true
+
+COPY . ./
+CMD ["/bin/sh", "/mount.sh"]