title: pyspark: create more than 1 dataframe fails
body: <p>I'd like to convert several large Pandas dataframes into Spark dataframes and then manipulate and merge them, as follows:</p>
  
  <pre><code>import pandas as pd
  from pyspark import SparkContext,SQLContext
  
  df1 = pd.read_csv('data1.cat',delim_whitespace=True)
  df2 = pd.read_csv('data2.cat',delim_whitespace=True)
  
  sc = SparkContext()
  sql = SQLContext(sc)
  spark_df1 = sql.createDataFrame(df1)
  spark_df2 = sql.createDataFrame(df2)
  </code></pre>
  
  <p>But something goes wrong, and I get the following error:</p>
  
  <pre><code>  File "/home/user/anaconda3/envs/conda_py3.6.8/lib/python3.6/site-packages/pyspark/sql/context.py", line 307, in createDataFrame
      return self.sparkSession.createDataFrame(data, schema, samplingRatio, verifySchema)
    File "/home/user/anaconda3/envs/conda_py3.6.8/lib/python3.6/site-packages/pyspark/sql/session.py", line 724, in createDataFrame
      data = self._convert_from_pandas(data, schema, timezone)
    File "/home/user/anaconda3/envs/conda_py3.6.8/lib/python3.6/site-packages/pyspark/sql/session.py", line 487, in _convert_from_pandas
      np_records = pdf.to_records(index=False)
    File "/home/user/anaconda3/envs/conda_py3.6.8/lib/python3.6/site-packages/pandas/core/frame.py", line 1839, in to_records
      return np.rec.fromarrays(arrays, dtype={"names": names, "formats": formats})
    File "/home/user/.local/lib/python3.6/site-packages/numpy/core/records.py", line 617, in fromarrays
      descr = sb.dtype(dtype)
  ValueError: name already used as a name or title
  </code></pre>
  
  <p>Is it possible to create multiple Spark dataframes in the same session like this?</p>