fence: Fix description and JSONRPC marshalling for fenceNode API

1) Fixes description of fenceNode return value
2) Fixes marshalling of fenceNode return value for JSONRPC

Change-Id: Ib39744828d56de2ec0bc6406d7dcfa116a7ec8d8
Bug-Url: https://bugzilla.redhat.com/1143860
Signed-off-by: Martin Perina <mperina@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/33034
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>