hdf5_chunking_query_bmr

[svn-r21113] Description:
    Revert the previous makefile change as release snapshot test failed with
    MANIFEST check. Don't clean 'testfiles' dir via 'make distclean' for 
    the case of build&test in source dir. 
    In regular daily testings, we build&test in seperate dir from source dir, 
    so no issues occurred. 
    However for the release snapshot test, it seems that we build&test in 
    source dir.
    The previous change can remove testfiles in source dir if build&test is 
    done in source dir becasue currently the dir name 'testfiles' is same in
    source dir and test dir. 
    Other task (7602) may change to use different name for the test directory,
    so 'make distclean' can do its job without interrupting MANIFEST.