title: DataFrame bar plot in subplots doesn't show xlabels
body: <p>I am trying to plot multiple subplots using the <code>DataFrame</code> <code>.plot()</code> function. It appears that the <code>xlabel</code> is appearing only in the last row.</p>
  
  <p><img src="https://i.stack.imgur.com/A91wb.png" alt="xlabel not appearing - example"></p>
  
  <pre><code>import pandas as pd
  import matplotlib.pyplot as plt
  fig, axs = plt.subplots(2,1)
  for ax in axs:
      df = pd.DataFrame(np.random.rand(1, 4), columns=['a', 'b', 'c', 'd'])
      df.index.name = 'Xlabel'
      df.plot(kind='bar', ax=ax)    
  plt.tight_layout()
  fig.show()
  </code></pre>
  
  <p>Is there any workaround for getting the <code>xlabel</code> in each row?</p>