broken dockerfile : github deploy key no longer copied correctly
<p>The following snippet worked fine a month ago (the last time i ran the container.)  It doesn't today.  Why? </p>

<pre><code>RUN mkdir /root/.ssh &amp;&amp; \
    mv /root/deployment_key /root/.ssh/id_rsa &amp;&amp;  cat /root/.ssh/id_rsa &amp;&amp; \
    chmod 600 /root/.ssh &amp;&amp; \
    chmod 600 /root/.ssh/id_rsa &amp;&amp; \
    ssh-keyscan github.com,$(getent hosts github.com | awk '{ print $1 }') &gt; ~/.ssh/known_hosts
</code></pre>

<p>When i <code>cat ~/.ssh/known_hosts</code>, the public key is only about half as long as it's supposed to be.  The private key is correct in <code>/root/.ssh/id_rsa</code>. </p>

<p>The next line (a <code>git clone</code> of a private repo) fails with </p>

<pre><code>Permission denied (publickey).
fatal: The remote end hung up unexpectedly
The command '/bin/sh -c git clone ssh://FOO@github.com/FOO/PRIVAT_REPO.git' returned a non-zero code: 128
</code></pre>

<p>I'm running docker Version 1.12.1-rc1-beta23 (build: 11375)  on OSX, but it fails on windows 10, too. </p>