JCLOUDS-356 multipart uploads with InputStream payloads

This changeset introduces an alternative to PayloadSlicer,
IterablePayloadSlicer, with a method for returning a Payload iterator.

...swift.blobstore.strategy.internal.SequentialMultipartUploadStrategy
has been updated to to use a payload iterator.
[JCLOUDS-263] Usage of internalURL services' endpoints