title: Push to docker repository fail on AzurePipelines
body: <p>The task <code>Docker push</code> fail to push the image into docker hub.</p>
  
  <p>The yml:</p>
  
  <pre><code>steps:
  - task: Docker@0
    displayName: 'Push an image'
    inputs:
      containerregistrytype: 'Container Registry'
      dockerRegistryConnection: 'docker hub'
      action: 'Push an image'
  </code></pre>
  
  <p>The log:</p>
  
  <pre><code>Starting: Push an image
  ==============================================================================
  Task         : Docker
  Description  : Build, tag, push, or run Docker images, or run a Docker command
  Version      : 0.157.0
  Author       : Microsoft Corporation
  Help         : https://docs.microsoft.com/azure/devops/pipelines/tasks/build/docker
  ==============================================================================
  dbef9fd1-06fb-47eb-af36-bf86b4d44152 exists true
  "C:\Program Files\Docker\docker.exe" push azuretp:38
  The push refers to repository [docker.io/library/azuretp]
  f2369ebe2bed: Preparing
  ...
  537ddf9b819a: Waiting
  denied: requested access to the resource is denied
  ##[error]C:\Program Files\Docker\docker.exe failed with return code: 
  </code></pre>
  
  <p>The connection <code>docker hub</code> is correct. I just reenter the credentials and Azure pipeline validate it successfully.</p>
  
  <p>The problem seams to be with the path, according to this <a href="https://stackoverflow.com/questions/41984399/denied-requested-access-to-the-resource-is-denied-docker">post</a>, but i can't find a way to specify my docker hub name within this task.</p>