LU-1994 llite: atomic_open support

LU-1994 llite: atomic_open support

v3.6 adds iop->atomic_open, to facilitate atomic lookup/create/open.
In the meantime, struct open_intent is removed from nameidata, and
->lookup()/->create() on longer carries intent data. So Lustre has
to support atomic_open in order to preserve intent functionality.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: Ibf4eee5a98c7a86417dc22b0075f647600328668
Reviewed-on: http://review.whamcloud.com/4387
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>