LU-1301 mgs: lu device for mgs

LU-1301 mgs: lu device for mgs

initial infrastructure to get lu-device for mgs:
device itself, support for objects, init/fini
old lvfs llog is still used to access on-disk data

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I46b2ba4bafa0f15970745ca024cd3239b9b63ec5
Reviewed-on: http://review.whamcloud.com/3674
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <tappro@whamcloud.com>