jsonrpc: StoragePool_updateVMs

Align naming between API.py and schema.

Change-Id: I26f7011b633c289f0d36bfd987f9392d2edf10f8
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35549
Reviewed-by: Oved Ourfali <oourfali@redhat.com>
Reviewed-by: Adam Litke <alitke@redhat.com>