vdsm: extend image over jsonrpc

Schema file was not consistend with API.py. All the verbs should use
the same constructor param names as it is defined in API.py.

Bug-Url: https://bugzilla.redhat.com/1113670
Change-Id: I437a23e04f97fb89eb4cd5646b73d9b1bddf240a
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/29359
Reviewed-by: Oved Ourfali <oourfali@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>