DirectRow.commit() should return response state

[ryanyuan]

When I run direct_row.commit(), I thought it succeeded but it didn't. It didn't give me any responses saying the error code or something. It turned out that I was using a wrong column family ID.

The behaviour of DirectRow.commit() should return a response status, same as Table.mutate_rows() because DirectRow.commit() actually calls Table.mutate_rows().