LU-909 osd: changes to osd api

LU-909 osd: changes to osd api

the main purpose of the patch is to get declare methods in the API
and to teach osd-based devices to use that

- new declaration methods for each changing method
- explicit destroy method:
  ->do_ref_del() never destroy object
- methods to access data in 0-copy manner:
  no actual implementation in this patch
- mdd/fld use new methods to create/declare/start transactions
- specific method to change/access version are removed:
  use xattr methods
- ldiskfs osd tracks all declarations and asserts if caller
  is trying to call changing method w/o proper declaration

Change-Id: I473c0c2950c1920abb2fef1dac465c08f35522ea
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Signed-off-by: Hongchao Zhang <hongchao.zhang@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1669
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>