Enable bash completion in build environment

Installs and configures bash completion for Docker.
Note that bash completion still has to be initialized by a custom
.bashrc file.

Signed-off-by: Harald Albers <github@albersweb.de>

Dockerfile

@@ -31,6 +31,7 @@ RUN apt-get update && apt-get install -y \
 	apparmor \
 	aufs-tools \
 	automake \
+	bash-completion \
 	btrfs-tools \
 	build-essential \
 	curl \
@@ -142,6 +143,9 @@ ENV DOCKER_BUILDTAGS apparmor selinux btrfs_noversion
 # Let us use a .bashrc file
 RUN ln -sfv $PWD/.bashrc ~/.bashrc
 
+# Register Docker's bash completion.
+RUN ln -sv $PWD/contrib/completion/bash/docker /etc/bash_completion.d/docker
+
 # Get useful and necessary Hub images so we can "docker load" locally instead of pulling
 COPY contrib/download-frozen-image.sh /go/src/github.com/docker/docker/contrib/
 RUN ./contrib/download-frozen-image.sh /docker-frozen-images \