jsonrpc: VM_getDiskAlignment

Align naming between API.py and schema.

Change-Id: Ia5b42a756c3171d5317df70e197ccc0809a37ecf
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35550
Reviewed-by: Oved Ourfali <oourfali@redhat.com>
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>