title: Trigger river update elasticsearch
body: <p>I have an elastic search river setup using the jdbc river plugin, that just does a simple select * from and indexes that table.</p>
  
  <p>But I would like to be able to trigger the river on demand via the API as well as at a standard time interval, so that I can have it index a document when its inserted into this table.</p>
  
  <p>Anybody know if theres anyway to do this at present? </p>
  
  <p>i.e. 
  <code>/_river/my_river/_refresh</code></p>
  
  <p>Thanks.</p>