title: Resetting index to flat after pivot_table in pandas
body: <p>I have the following dataframe <code>df</code></p>
  
  <pre><code>           Datum    HH  DayPrecipitation
  9377    2016-01-26  18  3
  9378    2016-01-26  19  4
  9379    2016-01-26  20  11
  9380    2016-01-26  21  23
  9381    2016-01-26  22  12
  </code></pre>
  
  <p>Which I converted to wide format using </p>
  
  <pre><code>df.pivot_table(index = 'Datum', columns='HH' ,values = 'DayPrecipitation')
  </code></pre>
  
  <p>This  leaves me with a double column</p>
  
  <pre><code>     HH     18  19  20  21  22
    Datum                 
  2016-01-26  3   4   11  23  12
  </code></pre>
  
  <p>I want to make the column look like this and rename the columns:</p>
  
  <pre><code>   Datum  col1 col2  col3 col4 col5 col6            
  2016-01-26  1    3    4    11   23   12
  </code></pre>
  
  <p>However when I use <code>reset_index</code> it just adds another index column and does not remove the multi_index. 
  Does anyone know how to achieve said table? Help would be much appreciated!</p>