test: add test-domain-exit-dispose-again back

d1ba82af1c2528c71e1b6b6a57844a7519b66ccb "fixed"
test-domain-exit-dispose-again by changing its logic to test that
process.domain was cleared properly in case an error was thrown from
a timer's callback.

However, it became clear when reviewing a recent change that refactors
lib/timers.js that it was not quite the intention of the original test.

Thus, this change adds the original implementation of
test-domain-exit-dispose-again back, with comments that make its
implementation easier to understand.

It also preserves the changes made by
d1ba82af1c2528c71e1b6b6a57844a7519b66ccb, but it moves them to a new
test file named test-timers-reset-process-domain-on-throw.js.

PR: #4278
PR-URL: https://github.com/nodejs/node/pull/4278


Reviewed-By: James M Snell <jasnell@gmail.com>