respondd module / olsrdhelper borked

[mkg20001]

• respondd module passes process fd to json-c, but if the process segfaults json-c call never finishes
  • use waitpid to check if process died, then pass fd to json-c (if it's possible to just queue up the data in memory... if it fails it shouldn't have written anything to stdout so no extra cleanup needed)
• libolsrdhelper / respondd doesn't handle request failures correctly
• libolsrdhelper doesn't retry
• raise limits in olsrv1+v2 parallel connections to something like 3 or 5 per second to hit the limit less often on slower machines

note: this is the primary cause behind status-page 500 errors on experimental