plain store: remove unnecessary check

Even for inode object, we can use O_DIRECT if request is aligned.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
collie: add terminator for cluster snapshot

Or we'll have following wrong output

yliu@K55VM-ubuntu:~/sheepdog$ collie/collie cluster snapshot
Usage: collie cluster snapshot {save|list|load|force|enable|disable} [-a address] [-p port] [-h] <tag|idx> <path>
Available subcommands:
  save                    save snapshot to localpath
  list                    list snapshot of localpath
  load                    list snapshot of localpath
  force                   force recover cluster immediately
  enable                  enable automatic recovery and run once recover if necessary
  disable                 disable automatic recovery
Options:
  -a, --address           specify the daemon address (default: localhost)
  -p, --port              specify the daemon port
  -h, --help              display this help and exit

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>