title: "Fail to execute ES search request" popup alert in SonarQube web UI after upgrading from 4.5.1 to 5.1
body: <p>when I click on an issue in SonarQube web UI to see details, I get this red popup:</p>
  
  <blockquote>
    <p>Fail to execute ES search request
    '{"size":1000,"query":{"bool":{"must":[{"term":{"fileUuid":"9c1ae181-f5c3-47da-8fad-3716aca54b6d"}},{"range":{"line":{"from":1,"to":1000,"include_lower":true,"include_upper":true}}}]}},"sort":[{"line":{"order":"asc"}}]}'
    on indices '[sourcelines]' on types '[sourceline]'</p>
  </blockquote>
  
  <p>and the source code or issue details are not shown.
  we started getting this after upgrading from Sonar 4.5.1 to 5.1</p>
  
  <p>I stopped the sonar server, deleted SONAR_QUBE/data/es folder, restarted the process and I see these messages in log:</p>
  
  <blockquote>
    <p>es[o.e.c.r.a.decider]  [sonar-1431655214631] low disk watermark
    [15%] exceeded on [1rprlr2pTS2zotdYv71GkQ][sonar-1431655214631] free:
    534.3mb[13.2%], replicas will not be assigned to this node</p>
  </blockquote>
  
  <p>I suppose this may be related, but not sure if these "replicas" have anything to do with "indices"...</p>