Make S3 GetObject test read in chunks
Make S3 GetObject test read in chunks

The actual test remains the same, but reading in chunks instead of the
whole object at a time actually tests the streaming a bit more.

DualSpark/rusoto,SecurityInsanity/rusoto,DualSpark/rust-aws,mattico/rusoto,mattico/rusoto,rusoto/rusoto,DualSpark/rust-aws,rusoto/rusoto,SecurityInsanity/rusoto,DualSpark/rusoto,rusoto/rusoto,DualSpark/rusoto,DualSpark/rust-aws,mattico/rusoto