Test default config modified to set logfile to empty string.

Required because of recent changes in the way logfile is set to standard
output.

tests/assets/default.conf

@@ -6,7 +6,7 @@ pidfile /var/run/redis.pid
 port 6379
 timeout 0
 loglevel verbose
-logfile stdout
+logfile ''
 databases 16
 
 save 900 1