IMPALA-1149: read bytes fields as strings in HdfsAvroScanner::MaterializeTuple()

Hive converts "bytes"-type fields to an array<tinyint> column, which
we can't even load the metadata for. However, if a bytes field appears
in a file schema but not the table schema, this change allows us to
read (but not materialize) the field. Otherwise we can't read the file
at all.

This change also adds a "bytes"-type field to one of the files in
functional_avro_snap.schema_resolution_test.

Change-Id: I25953ee049e174fc4dbff5d68520a6f87e545339
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3823
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins