remove use of [core] domain module - due to it being deprecated

[iamjochem]

the domain module is marked as deprecated (see here), I think it is wise to remove it.

Removing it's usage does not have any effect on normal shutdown operation.

Given that uncaught exceptions should be treated as a stop-the-world situation and we are already shutting down in this context I feel that no love is lost.

What do you think?

[suprememoocow]

Thanks for the PR, but one of the tests is failing:

  1) shutdown-coordinator should deal with stages that error:
     Uncaught
  Error
      at Timeout._onTimeout (tests/shutdown-coordinator-test.js:60:15)
      at ontimeout (timers.js:365:14)
      at tryOnTimeout (timers.js:237:5)
      at Timer.listOnTimeout (timers.js:20

This test specific tests the case where a shutdown handler throws an unhandled/uncaught exception. Because we're running this code from inside a domain, we're able to recover from it. Offhand, I'm not sure what the best non-domain alternative for this situation is.