Set working directory for redis-server to /var/lib/redis

This commit changes the working directory used for the redis-server
process from /etc/redis, which the redis user does not have write access
to, to /var/lib/redis, which is writable by the redis user.

container/supervisord.conf

@@ -19,7 +19,7 @@ command=/usr/bin/mysqld_safe
 
 [program:redis-server]
 process_name = redis-server
-directory = /etc/redis
+directory = /var/lib/redis
 command=/usr/bin/redis-server /etc/redis/redis.conf
 user=redis