jsonrpc: diskSizeExtend missing in command_info

Bug-Url: https://bugzilla.redhat.com/1161115
Change-Id: I099b83defd9fc3f0280ddeb28f3c4b706f8998c2
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/35218
Reviewed-by: Oved Ourfali <oourfali@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>