Support index shifting for struct fields

In HIVE-13873, the following case doesn't work:

select s.c from tbl

where tbl is of schema:

a                   	int
s                   	struct<b:int,c:string>

This is because currently we generate a "pruned" schema (in terms of GroupType) for Parquet reader to scan the data. However, on the Hive side the object inspector still uses the original schema. In particular, in this case for s.c the data returned by Parquet reader is in index 0, but the object inspector tries to read it in index 1. Therefore, in correct result will be returned.