title: no suitable node - unable to deploy image using docker service
body: <p>I  have a docker swarm based on raspberry pi 3. I have 3 nodes. I have created an image on my laptop and pushed that to the docker registry. </p>
  
  <p>If I try to start the image on a node in the swarm using docker run it works as expected. </p>
  
  <pre><code>docker run -ti alexellis2/pi-sharp:0.1
  </code></pre>
  
  <p>but if i try and start it using a docker service it fails. </p>
  
  <pre><code>docker service create --name test alexellis2/pi-sharp:0.1
  </code></pre>
  
  <p>Error
       1/1: no suitable node (unsupported platform on 3 nodes)</p>
  
  <p>If I do an docker inspect on the service it shows this information. </p>
  
  <pre><code>"Placement": {
                      "Platforms": [
                          {
                              "Architecture": "amd64",
                              "OS": "linux"
                          }
                      ]
                  },
  </code></pre>
  
  <p>I have tried to prune containers and images to no avail. </p>
  
  <p>My question is why am I able to use the image using docker run but not using docker service?</p>