title: docker pull from Artifactory results in "net/http: request canceled" inconsistently
body: <p>We are running Artifactory 5.11.0 (just update to 6.0.2 today and haven't yet seen this) in a docker container and when our automation executes a <code>docker pull</code> from Artifactory, 9/10 times it is successful.  Sometimes, even when running the <code>docker pull</code> from the machine hosting Artifactory, the <code>docker pull</code> fails with:</p>
  
  <blockquote>
    <p>Pulling 'docker.{artifactory url}/staging:latest'...
    Error response from daemon: Get <a href="http://docker" rel="nofollow noreferrer">http://docker</a>.{artifactory url}/v2/staging/manifests/latest: Get <a href="http://docker" rel="nofollow noreferrer">http://docker</a>.{artifactory url}:80/artifactory/api/docker/docker/v2/token?account=admin&amp;scope=repository%3Astaging%3Apull&amp;service=docker.{artifactory url}%3A80:
    net/http: request canceled (Client.Timeout exceeded while awaiting
    headers)</p>
  </blockquote>
  
  <p>Like I said, most of the time this is working perfect, but that 1/10 (probably less) we get the above error during our automated builds.  I tried running the <code>docker pull</code> in a while loop over night until it hit a failure and there was no failure.  Ran ping overnight and no packets were lost.</p>
  
  <p>OS: Debian 9 x64<br>
  Docker version 17.09.0-ce, build afdb6d4 and seems to happen more frequently with Docker version 18.03.1~ce-0~debian, but I have no direct evidence to suggest the client is at fault.</p>