Branch HEAD

 b=12521
 - set Lustre hints (except striping hints) "anywhere"
 - perform collective I/O for interleaving, no matter how big the req size is
 - keep the semantic information of cb_nodes
 - perform collective I/O by the same client if the whole file access portion
   is no bigger than stripe size and cb_nodes is changed by the user
 - fix some bugs in the error handling
 - remove redundant codes