LU-3279 changelog: fix CL_LAYOUT, accept all types

In order to avoid compatibility issues with older ChangeLog consumers,
change the new CL_LAYOUT record to use the value previously assigned
to CL_IOCTL.  The CL_IOCTL type was never used anywhere, and it didn't
really make any sense as a ChangeLog record, since it could really
mean anything at all.

The changelog_show_cb() function is renamed to changelog_kkuc_cb(),
since it is really about consuming the ChangeLog and passing it up to
the kernel-user-coms interface.  At some point we should consider to
implement a DBUS-based ChangeLog interface as well.

The changelog_kkuc_cb() "sanity check" on cr_type was removed, since
there is no reason the client kernel needs to know every record type
that is being passed to userspace.  It is up to the client tool to
determine what records that it can process.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Id8e6471827a89d8c62808e6b3cfd9693d6026431
Reviewed-on: http://review.whamcloud.com/6308
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Tested-by: Hudson
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>