Test for [first N] issue in ExHdfsScanTcb (hive)

This change simply adds a testcase for processing of GET_N
in ExHdfsScanTcb, in cases where the operator scans multiple
parts of an HDFS file.

Change-Id: I78cf9d43eab57215f38dcf3e1fe7b2e18e8b1301
Merge "Test for [first N] issue in ExHdfsScanTcb (hive)"