Calculate and include SHA-1 hash at the end of a B2 upload

B2 removed the need to calculate the SHA-1 hash before uploading a file, allowing streaming. Currently jclouds uploads files without a hash, although B2 also supports calculating the hash while uploading then including the SHA-1 at the end via X-Bz-Content-Sha1: hex_digits_at_end:

https://www.backblaze.com/b2/docs/uploading.html

Supporting this requires some changes to jclouds to allow modifying the Payload to emit the hash at the end of the transfer.