bug mpi write create  multi files  

Change-Id: Ia3bf8d65dbf02bff6b912e48119465c79035c1cc
Signed-off-by: YU Zhi <yuzhi@ipp.ac.cn>
fix bug DataStream::open_file

Change-Id: I09475cfcdc02904e18c288209d0970631eeae939
Signed-off-by: YU Zhi <yuzhi@ipp.ac.cn>