Allow tests to access query result column values by col alias or col position

For example, you can now do something like:
result_set = execute("select * from tbl")
result_row = result_set[0]
result_row['col_alias'] or result_row[4]

to access column values. If the column alias/position does not exist an exception is
thrown.

Change-Id: Ie4b65619ed17fd90bf39e0966a7fc7e1180dbc5c
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2719
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>
Tested-by: jenkins