* DistCp to support checksum validation when copy blocks in parallel * address review comments * add checksums comparison test for combine mode (cherry picked from commit c765584eb231f8482f5b90b7e8f61f9f7a931d09)
* DistCp to support checksum validation when copy blocks in parallel * address review comments * add checksums comparison test for combine mode (cherry picked from commit c765584eb231f8482f5b90b7e8f61f9f7a931d09)