Not including consumer.properties and producer.properties in /etc/kafka.

The old kafka-consumer-shell.sh and kafka-producer-shell.sh scripts have
been removed from upstream 0.8 bin/.  These were the only scripts that
used these property files.  kafka-console-consumer.sh and
kafka-console-producer.sh set properties using CLI options.

However, the kafka mirror command (and /etc/init.d/kafka-mirror) takes
multiple consumer.*.properties and a single producer.properties file.
These are expected to be in /etc/kafka/mirror.  These two property
which still (for some reason) remain in 0.8's config/ directory
are installed into /etc/kafka/mirror (by debian/kafka.install) as
example files which the user should edit and rename in order to
use kafka mirror.

Also fixing kafka-mirror.init so that it checks for
$KAFKA_MIRROR_CONSUMER_CONFIGS properly.

Change-Id: I2c31fe67b95c34d1b704dce40bdaf45a4f8fb784