LU-1302 llog: modify llog_write/llog_add to support OSD

LU-1302 llog: modify llog_write/llog_add to support OSD

- add transaction and declarations in API to work over OSD
- change logic in llog catalog to open plain llogs during
  declarations
- keep lop_obd_add to work via chain of obds, e.g. MDS-LOV-OSC.
  It will be not needed with LOD/OSP anymore

Signed-off-by: Mikhail Pershin <tappro@whamcloud.com>
Change-Id: Ifba546fcb5fe8434fd4aa21a21b831737df73729
Reviewed-on: http://review.whamcloud.com/3923
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>