title: centos7 cockpit 176 can't add remote hosts
body: <p>I set up a 01-machines.json with one host (server0), I can ssh to server0 from the management node (master0). I get an error in the UI  saying <code>A compatible version of Cockpit is not installed on 192.168.66.17.</code>  It has the same exact version, so the error is misleading. I  can reach the UI on server0:9090 with the same creds (cockpit/<strong><em>password</em></strong>), no that isn't the password.</p>
  
  <pre><code>{
          "server0": {
            "address": "192.168.66.17",
            "visible": true,
            "color": "green"
        }
  }
  </code></pre>
  
  <p>I don't see anything in the logs on master0 or server0 to see what is happening.  The user I  connect with in  the UI is the same on server0, it is in the wheel  group and has passwordless sudo</p>
  
  <pre><code># ssh cockpit@192.168.66.17
  cockpit@192.168.66.17's password: 
  Last login: Wed Oct 24 14:16:18 2018 from 192.168.0.20
  [cockpit@app-node-0 ~]$ sudo su -
  Last login: Wed Oct 24 14:16:58 UTC 2018 on pts/1
  [root@app-node-0 ~]# 
  </code></pre>