=clu #3826 Harden cluster.StressSpec

* The Identify message didn't get through to the master, which
  was stopping at the same time, and it didn't got redirected to
  deadletters, i.e. the "termination race"
Merge pull request #1942 from akka/wip-3826-cluster.StressSpec-patriknw

=clu #3826 Harden cluster.StressSpec