LU-1711 mount: lu_site is provided by OSD

LU-1711 mount: lu_site is provided by OSD

previously it was created by MDT, which is started after MGS.
so we relocate lu_site in OSD and now it's created before
any service like MDS/MGS.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I43312218c293df509064cc6a854074e652a6e691
Reviewed-on: http://review.whamcloud.com/3651
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>