title: DOCKER_OPTS do not work in config file /etc/default/docker
body: <p>I have changed <code>/etc/default/docker</code> with <code>DOCKER_OPTS="-H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock"</code> (docker version 1.4.1 in ubuntu 14.04), but it do not take any effect for me (not listening at port <code>2375</code>). It seems that docker do not read this initial config file because I found <code>export http_proxy</code> enviroment do not work too.</p>
  
  <p>Only <code>sudo docker -H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock -d</code> works.</p>
  
  <p>It really confused me!</p>