Rebalance fails completely silently when no ns_orchestrator process is running

We do have error in logs:

Server error during processing: ["web request failed",

{path,"/controller/rebalance"}

,

{type,exit}

,
{what,
{noproc,
{gen_fsm,sync_send_event,
[

{global,ns_orchestrator}

,

{start_rebalance, ['ns_1@10.2.1.12','ns_1@10.2.1.50'], ['ns_1@10.2.1.13'], []}

]}}},
{trace,
[

{gen_fsm,sync_send_event,2}

,

{menelaus_web,do_handle_rebalance,3}

,

{menelaus_web,loop,3}

,

{mochiweb_http,headers,5}

,

{proc_lib,init_p_do_apply,3}

]}] (repeated 5 times)

But:

a) we probably shouldn't send 500 (not sure about that)
b) we definitely should react on that 500 in UI