title: Dockerfile pull from nexus repository
body: <p>My dockerfile points to a private nexus repository
  <code>FROM nexus-repo/image:latest</code>
  when i try and build i get a<code>Could not build image: received unexpected HTTP status: 503 Service Unavailable</code></p>
  
  <p>I am logged in beforehand, and running <code>docker pull nexus-repo/image:latest</code> works okay. What could be the cause of this problem?</p>