title: ValidationMonitor triggered only once
body: <p>I am trying to use Tensorflow's <code>ValidationMonitor</code> on <code>DNNRegressor.fit</code> </p>
  
  <p>but it gets triggered only once when <code>global_step = 1</code>. How to fix it?</p>
  
  <p>The <code>every_n_step</code> setup to 1 like this</p>
  
  <pre><code>validation_monitor = tf.contrib.learn.monitors.ValidationMonitor(
      test_dataset.data,
      test_dataset.target,
      every_n_steps=1)
  
  regressor = tf.contrib.learn.DNNRegressor(feature_columns=feature_columns,
                                              hidden_units=[2],
                                              model_dir="/home/maciej/tf-logs")
  
  
  regressor.fit(x=train_dataset.data,
                 y=train_dataset.target,
                 steps=1000, 
                 monitors=[validation_monitor])
  </code></pre>
  
  <p>What I get on stdout are logs about loss and a single one about validation:</p>
  
  <pre><code>INFO:tensorflow:Saving dict for global step 201: global_step = 201, loss = 5.50003
  INFO:tensorflow:Validation (step 201): loss = 5.50003, global_step = 201
  INFO:tensorflow:global_step/sec: 96.1045
  INFO:tensorflow:loss = 6.3935, step = 301
  INFO:tensorflow:global_step/sec: 154.978
  INFO:tensorflow:loss = 4.77587, step = 401
  INFO:tensorflow:global_step/sec: 158.06
  INFO:tensorflow:loss = 3.72956, step = 501
  INFO:tensorflow:global_step/sec: 151.51
  INFO:tensorflow:loss = 3.04578, step = 601
  </code></pre>
  
  <p>This is also confirmed on tensorboard.</p>
  
  <p>The full code and logs are available here:
  <a href="https://gist.github.com/maciejjaskowski/9f791e517f379c41d20cc72619909fe6" rel="nofollow noreferrer">https://gist.github.com/maciejjaskowski/9f791e517f379c41d20cc72619909fe6</a></p>