jsonrpc: VM_updateVmPolicy

Align naming between API.py and schema.

Change-Id: I39c3e0a675b0574c25a2602f672ed6a36a05547c
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35556
Reviewed-by: Adam Litke <alitke@redhat.com>