jsonrpc: VM_setIoTune

Align naming between API.py and schema.

Change-Id: I6a4827dd6dac84eed0430ee6e433f1b0b403dd81
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35554
Reviewed-by: Martin Sivák <msivak@redhat.com>
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>