fix(balancer) use a FIFO for eventual consistency updates

* When using eventual worker consistency, instead of trying to
  synchronize all workers using a shared dictionary, share the events
  and let each worker deal with its updates.
* Fix several IPv6 issues in balancer tests.
* Balancer stress tests file was renamed, so the tests must be ran on
  demand from now on, as they take a long time to run and most of them
  seem to be flaky on CI environment.