=clu #3973 Make JoinSeedNodeProcess actor name unique

* These names are not used, but for debuggability I prefer real names

(cherry picked from commit 1f2be54eebe5feb2f82c2659c8262f1db8343125)
Merge pull request #2118 from akka/wip-3973-joinSeedNodeProcess-name-master-patriknw

=clu #3973 Make JoinSeedNodeProcess actor name unique (forward port)