Do not fake /bin/bash, just use the real bash

Looks like 0.6, we ended up with dash as the default shell, with
/bin/sh as well as /bin/dash ending up invoking dash.

We should not change the contract by faking a link to /bin/bash.
Let's install the actual bash package and make sure /bin/sh is
linked to /bin/bash as well.

build/debian-hyperkube-base/Dockerfile

@@ -14,10 +14,13 @@
 
 FROM BASEIMAGE
 
+RUN echo CACHEBUST>/dev/null && clean-install \
+    bash
+
 # The samba-common, cifs-utils, and nfs-common packages depend on
-# ucf, which itself depends on /bin/bash existing.
-# It doesn't seem to actually need bash, however.
-RUN ln -s /bin/sh /bin/bash
+# ucf, which itself depends on /bin/bash.
+RUN echo "dash dash/sh boolean false" | debconf-set-selections
+RUN DEBIAN_FRONTEND=noninteractive dpkg-reconfigure dash
 
 RUN echo CACHEBUST>/dev/null && clean-install \
     ca-certificates \

build/debian-hyperkube-base/Makefile

@@ -19,7 +19,7 @@
 
 REGISTRY?=gcr.io/google-containers
 IMAGE?=debian-hyperkube-base
-TAG=0.7
+TAG=0.8
 ARCH?=amd64
 CACHEBUST?=1