Improve graceful shutdown for Op-rbuilder

[ferranbt]

Add a graceful shutdown to the op-rbuilder that:

• op-rbuilder receives the termination signal (SIGINT or SIGTERM)
• if it is not building block (didn't receive FCU with attributes) => close conns and ports and shutdown
• if it is building block (did receive FCU with atttributes that was not yet matched with consecutive getPayload)
  • stop accepting further FCUs with attrs
  • wait until getPayload came in, or 2x block-time (whichever comes first)
  • close conns and ports and terminate

Some of these we already handle.

(cc @0x416e746f6e)

[SozinM]

@therustmonk is working on it

[therustmonk]

@SozinM Yes, I'm currently working on this, so you can assign this task to me.