Add test for config of multiple loggers, see #2968
(cherry picked from commit 14d857a593513d932b82ab2fd4e2a2dc78ef911c)

Conflicts:

	akka-actor-tests/src/test/scala/akka/event/LoggerSpec.scala
Merge pull request #1180 from akka/wip-2968-test-many-loggers-master-patriknw

Add test for config of multiple loggers, see #2968