Putting kafka log data dir in a subdir of the mount points.

lost+found makes Kafka unhappy:

http://mail-archives.apache.org/mod_mbox/kafka-users/201305.mbox/%3CCAF8-MNeyz3orYKXeNkV8YYVZ=6tHJHSWWcWTHtsF_arGYBmTeA@mail.gmail.com%3E

Change-Id: I8f3ea193b151ca499cfaaef012013a15a5d08345