LU-3279 changelog: fix CL_LAYOUT comment, string

LU-3279 changelog: fix CL_LAYOUT comment, string

Fix the CL_LAYOUT comment, since it is possible that layout swap
could be used in cases where the file content is changed.  I don't
think there are any real world use cases for this, but that depends
on what tools are being used on the filesystem.

Also change the "LAYOUT" string for this ChangeLog record type to
be "LYOUT" to match the convention of other strings to only be
5 characters long.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ibf9a57216e0c45a1e15cef9cfe5ee7f509500c1e
Reviewed-on: http://review.whamcloud.com/6338
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>