text: Title: Pandas DataFrame to Hadoop using Hive and Impala uses incorrect data type
  Body: # In short, issue is that SQLAlchemy seems to be trying to create following, and error is that type TEXT should be type STRING or VARCHAR
  
  CREATE TABLE test_pandas_to_hive (
  	index BIGINT, 
  	name TEXT
  )
  
  
  # Code starts here
  
  import pandas as pd
  from sqlalchemy import *
  from sqlalchemy.engine import create_engine
  from sqlalchemy.schema import *
  
  # Connection to Impala Hadoop
  engine = create_engine(
      'impala://<my_org_url>',
      connect_args={'port': <my_org_port>,
                    'auth_mechanism': 'GSSAPI',
                    'database': 'my_db_scratch_space'},
  )
  
  # Simple dataset
  df = pd.DataFrame({'name' : ['User 1', 'User 2', 'User 3']})
  
  # Now write to Hadoop
  df.to_sql('test_pandas_to_hive', con=engine)
  
  
  # Get the following error, seems to be trying to create a table in Hadoop, but the data type is wrong
  # Is trying to create a column of data type 'text', which doesn't exist
  # Should be of data type 'string' or 'varchar' instead
  
  ---------------------------------------------------------------------------
  HiveServer2Error                          Traceback (most recent call last)
  ~/.conda/envs/Python3venv/lib/python3.6/site-packages/sqlalchemy/engine/base.py in _execute_context(self, dialect, constructor, statement, parameters, *args)
     1243                     self.dialect.do_execute(
  -> 1244                         cursor, statement, parameters, context
     1245                     )
  
  ...
  
  ~/.conda/envs/Python3venv/lib/python3.6/site-packages/impala/hiveserver2.py in err_if_rpc_not_ok(resp)
      702             resp.status.statusCode != TStatusCode.SUCCESS_WITH_INFO_STATUS and
      703             resp.status.statusCode != TStatusCode.STILL_EXECUTING_STATUS):
  --> 704         raise HiveServer2Error(resp.status.errorMessage)
      705 
      706 
  
  DBAPIError: (impala.error.HiveServer2Error) AnalysisException: Syntax error in line 4:
  	name TEXT
        ^
  Encountered: IDENTIFIER
  Expected: ARRAY, BIGINT, BINARY, BOOLEAN, CHAR, DATE, DATETIME, DECIMAL, REAL, FLOAT, INTEGER, MAP, SMALLINT, STRING, STRUCT, TIMESTAMP, TINYINT, VARCHAR
  
  CAUSED BY: Exception: Syntax error
  
  [SQL: 
  CREATE TABLE test_pandas_to_hive (
  	index BIGINT, 
  	name TEXT
  )
  
  ]
  (Background on this error at: http://sqlalche.me/e/dbapi)
  
  