Work around issue in the docker index

The docker index is affected by
<moby/moby#6345 (comment)>.
This fix is an attempt at at temporary workaround and should be
reverted once the docker version behind the registry is updated at the
next release.

Dockerfile

@@ -16,9 +16,12 @@ MAINTAINER Homme Zwaagstra <[email protected]>
 # Ensure the package repository is up to date
 RUN apt-get update -y
 
+# Temporarily hack around a docker build issue. See
+# <https://github.com/docker/docker/issues/6345#issuecomment-49245365>.
+RUN ln -s -f /bin/true /usr/bin/chfn
+
 # Install basic dependencies
 RUN apt-get install -y \
-    apt-utils \
     software-properties-common \
     python-software-properties \
     build-essential \