Use Guzzle Streams instead of implementing own streams

Summary:
There is a Stream implementation that is already
used by Guzzle. Instead of implementing an own Stream
Interface the implementation of Guzzle should be used.
http://docs.guzzlephp.org/en/latest/streams.html

Depends on D455

Reviewers: #forgetit-dev, dkd-doan, claus.due

Reviewed By: #forgetit-dev, dkd-doan, claus.due

Differential Revision: https://phabricator.dkd.de/D456