Fix exception logging

According to the akka logging documentation, Throwable should come
first in the parameters.

http://doc.akka.io/api/akka/2.0/akka/event/LoggingAdapter.html

Change-Id: I88bd38d35becde29b7b325b9e0f9295ea1c671c6
Merge pull request #864 from iven/logger_fix

Fix exception logging