Improves S3 integration test by ensuring obj payload has contents.
Improves S3 integration test by ensuring obj payload has contents.

mthjones/rusoto,DualSpark/rust-aws,SecurityInsanity/rusoto,mattico/rusoto,DualSpark/rusoto,SecurityInsanity/rusoto,rusoto/rusoto,mattico/rusoto,mattico/rusoto,ford-prefect/rusoto,DualSpark/rust-aws,mthjones/rusoto,DualSpark/rusoto,rusoto/rusoto,rusoto/rusoto,DualSpark/rusoto,DualSpark/rust-aws,ford-prefect/rusoto