Fix v2 data upload to swift

An upload of image data via the v2 api when using a swift backend would
stacktrace with 'UnsupportedOperation: seek'.

Wrap the data in a CooperativeReader to both 1) fix this issue and 2) reap
the multi-threaded 'sheduling fairness' benefit of the CooperativeReader.

Fix for bug 1147231.

Change-Id: I604c67d2d6ecd77a12e11b2f641edb4095c4bb60
Merge "Fix v2 data upload to swift"