SEQUENCEFILE: Add support for writing sequence files.

This supports both uncompressed and block compressed formats. Row compressed formats are
not supported. The type of compression is specified using a query parameter
COMPRESSION_CODEC with values NONE, GZIP, BZIP2, and SNAPPY.

Note: this patch only has basic testing. More extensive testing will be done when this
avro writer is used in data loading.

Change-Id: Id284bd4f3a28e27e49d56b1127cdc83c736feb61
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3541
Reviewed-by: Victor Bittorf <victor.bittorf@cloudera.com>
Tested-by: jenkins