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
Reviewed-On: http://gerrit.ovirt.org/#/c/29359/
Change-Id: I2debb5dde386032af904877baf2a6e58eddfb2c5
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/29857
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>