generate_objects: use rewind=True in upload_objects

Use the rewind=True argument when uploading objects to make
realistic.py's use of upload_objects compatible with boto>=2.4.1, which
will try to seek to the end of the fp if rewind is not True.
Revert "rgw: remove more fails_on_dho tags"

This reverts commit efa352711b2ebb9f7dbc85896c22c6123d33ae8b.
Revert "rgw: remove fails_on_dho tags"

This reverts commit 509715810d325b7f842bc31d34c307f8b8296f73.