LU-9771 flr: Send write intent RPC to mdt

LU-9771 flr: Send write intent RPC to mdt

When a mirrored file is going to be written, the client needs
to send a write intent RPC to the MDT. The MDT will pick a mirror
as primary and mark the others as stale. The new md operation
moo_layout_change() is introduced for this purpose. The MDT also
transfers the latest layout version to the OST objects via
do_attr_set().

Once OSTs receive the setattr RPC for layout version change, it
will set the update layout version into extended attribute
XATTR_NAME_FID.

Test-Parameters: testlist=sanity-flr
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ib0049a78b95895141b0032e8eff526a73a160dcb
Reviewed-on: https://review.whamcloud.com/29091
Tested-by: Jenkins
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>