Bulk Unload/extract  (prototype)

These changes add support for a bulk unload/extract (prototype) to unload data
from trafodion tables into HDFS. Bulk unload unloads  data in either
compressed (gzip) or uncompressed formats. When specified, compression take
place before writing data bufers to files. Once the data unloading is done
the files are merged into one single file. If compression is specified
the data are unloaded into files in compressed format and then merged in
compressed format. Otherwise they are unloaded in uncompressed format
and merged into one uncompressed file.

The unload syntax is:

 UNLOAD [[WITH option] [, option] ...] INTO <hive-table>  query_expression

Where
*<hive-table> is a hive table.
and
*option can be:
- PURGEDATA FROM TARGET:  When this option specfied the files under the
        <hive-table> are deleted
- COMPRESSION GZIP: when this option is specfied the Gzip compression is
        used. the compression takes place in the hive-insert node and data
        is written to disk in compressed format (Gzip i the only supported
        compression for now)
- MERGE FILE <merged_file-path>: When this option is specified the files
        unloaded are merged into one single file <merged-file-path>. if
        compressiion is specied the data unloaded in compressed format
        and the merged file will be in compressed formt also.
- NO OUTPUT: If this option is specified then no status messge is dispalyed

Change-Id: Ifd6f543d867f29ee752bcb80020c5ad6c16b7277