LU-3057 llite: swap layout fixes - hang at sanity 56x and 56w

Two issues will be fixed in this patch:
1. in ll_swap_layouts, ll_setattr() should be called with inode mutex
   held.
2. stripes should be reloaded after layout is swapped on the MDT.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ibdb30c78bf8642886afc7343544d7db3bcbe6726
Reviewed-on: http://review.whamcloud.com/5874
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>