LU-2182 llapi: implementation of new llapi_layout API

LU-2182 llapi: implementation of new llapi_layout API

Add a new set of llapi routines for interacting with file layouts that
hide the details of the wire-protocol data structures from the user.
Define an opaque struct llapi_layout to abstract the layout of a
lustre file and generic accessor functions to read and write it.  The
following documented functions are added the liblustreapi public
interface with accompanying man pages:

  llapi_layout_alloc - allocate a new layout
  llapi_layout_free - free memory allocated for a layout
  llapi_layout_file_create - create new file with given layout
  llapi_layout_file_open - open or create a file with given layout
  llapi_layout_get_by_path - get file layout given a path
  llapi_layout_get_by_fd - get file layout given a file descriptor
  llapi_layout_get_by_fid - get file layout given a Lustre FID
  llapi_layout_ost_index_get - get OST index associated with a stripe
  llapi_layout_ost_index_set - set OST index associated with a stripe
  llapi_layout_pattern_get - get RAID pattern of a layout
  llapi_layout_pattern_set - set RAID pattern of a layout
  llapi_layout_pool_name_get - get pool name of a layout
  llapi_layout_pool_name_set - set pool name of a layout
  llapi_layout_stripe_count_get - get stripe count of a layout
  llapi_layout_stripe_count_set - set stripe count of a layout
  llapi_layout_stripe_size_get - get stripe size of a layout
  llapi_layout_stripe_size_set - set stripe size of a layout

The layouts are read and written using fgetxattr() and fsetxattr()
instead of ioctl() to make it easier for architectures like Blue Gene
to function-ship the system calls.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I35fb51055b6438ef3090f43c28a4083a66eaa907
Reviewed-on: http://review.whamcloud.com/5302
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>