title: python etcd3 randomly fails with failed: grpc._channel._Rendezvous: <_Rendezvous of RPC that terminated with: status = StatusCode.UNKNOWN
body: <p>I have very simple setup. I have etcd 3.3 server. 
  I have code in python (3.6) ive installed etcd3 version 0.10.0</p>
  
  <pre><code>import etcd3
  data = etcd3.client(host='my.host.net', port=2379).get('/exesiting/key'))
  print( data )
  </code></pre>
  
  <p>Key exsist, server address is ok.
  This code fails randomly with follwing error</p>
  
  <pre><code>failed: grpc._channel._Rendezvous: &lt;_Rendezvous of RPC that terminated with:
          status = StatusCode.UNKNOWN
          details = "Failed to create subchannel"
          debug_error_string = "{"created":"@1557133790.170407000","description":"Failed to create subchannel","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":2715,"referenced_errors":[{"created":"@1557133790.170402000","description":"Empty update","file":"src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc","file_line":270}]}"
  </code></pre>
  
  <p>What is wrong? Do i need to clean up connections somehow?</p>