Make "node/status" request asynchronous

Avoid blocking dispatcher when long running cancel command arise (usually when RN are unreachable because of swap)
Clean asynchronous "cancel" webservice

- Standard cancel "/nodes/<id>/status" is now asynchronous
  A user defined timeout can be set when contacting running RNs.
  The requesting client (pulback) will still wait until the end of the whole cancel
  but other commands will be treated inbetween.

- New webservice is added: "/nodes/<id>/cancel to handle the specific cancel job case
  The server part (cleaning command in the list) is executed very quickly
  Then a thread is started to send cancel request to each running RNs in background
  Thus the client is not blocked until each RN has timed out.
  RNs that encounter a problem will still be cleaned and marked as "quarantine"