Log ActorInitializationException instead of underlying exception

We currently log the underlying exception of an ActorInitializationException since I screwed up porting this from AKKA JVM a week back. :)
We should only use the message from the underlying exception, and still log the entire ActorInitializationException.

This is important since it's otherwise impossible to test that ActorInitializationException is thrown.
Merge pull request #523 from HCanber/log-ActorInitializationException

Log ActorInitializationException instead of underlying exception