jsonrpc: Add timeout to JsonRpcTests:JsonRpcServerTests

Without it tasks linger forever if server fails to respond

Change-Id: Iba0d6f39b0a29df5cc08ae0ceff3d91c31a178f9
Signed-off-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/10250
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>