Shift to development track containerd

Move to the development track of `containerd` not the legacy 0.2
branch. The commands have changed a bit.

This does increase the image size as we are bundling the Docker
copy and our copy, and the new one is larger as it is growing features.
Hopefully Docker will shrink eventually. Also we may replace `ctr`
with a library.

Fix #1029

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

alpine/Dockerfile

@@ -11,11 +11,6 @@ RUN \
 
 COPY . .
 RUN rm Dockerfile
-RUN cd /usr/bin && \
-  ln -s docker-runc runc && \
-  ln -s docker-containerd-shim containerd-shim && \
-  ln -s docker-containerd-ctr containerd-ctr && \
-  ln -s docker-containerd containerd
 
 RUN \
   rc-update add sysctl boot && \