jsonrpc: Image_upload

Align naming between API.py and schema.

Change-Id: I1d3ec723ed062e7c2209cfaee657c8d81a1b5355
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35533
Reviewed-by: Adam Litke <alitke@redhat.com>