jsonrpc: Don't call server.shutdown since it doesn't exist

Change-Id: Ic8246b147fb4b6495f69923d4d44b5517d6ee6c5
Signed-off-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/10249
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>