generate_objects: use rewind=True in upload_objects
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.

Nexenta/s3-tests,ceph/s3-tests,jmunhoz/s3-tests,Intel-bigdata/s3-tests,andrewgaul/s3-tests,robbat2/s3-tests,jmunhoz/s3-tests,basho/s3-tests,piousbox/s3-tests,tobegit3hub/s3-tests,basho/s3-tests,Intel-bigdata/s3-tests,smithfarm/s3-tests,andrewgaul/s3-tests,ceph/s3-tests,tobegit3hub/s3-tests,Nexenta/s3-tests,smithfarm/s3-tests,SUSE/s3-tests,SUSE/s3-tests,Nexenta/s3-tests,piousbox/s3-tests,dreamhost/s3-tests,dreamhost/s3-tests,timuralp/s3-tests,piousbox/s3-tests,Nexenta/s3-tests,robbat2/s3-tests,timuralp/s3-tests