title: gdb in docker container returns "ptrace: Operation not permitted."
body: <p>I've checked <code>/proc/sys/kernel/yama/ptrace_scope</code> in the container and on the host - both report the value as zero but when attached to pid one gdb reports </p>
  
  <pre><code>Reading symbols from /opt/my-web-proxy/bin/my-web-proxy...done.
  Attaching to program: /opt/my-web-proxy/bin/my-web-proxy, process 1
  ptrace: Operation not permitted.
  </code></pre>
  
  <p>I've also tried attached to the container with the privileged flag</p>
  
  <pre><code>docker exec --privileged -it mywebproxy_my-proxy_1 /bin/bash
  </code></pre>
  
  <p>Host OS is Fedora 25 with docker from their repos and container is a official centos6.8 </p>