dog: size_to_str -> strnumber

And make strnumber() take only one parameter instead of lengthy 3.

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

Add a new struct sd_stat to monitor the activities of the sheep daemon, which
are read by the dog. Currently it is very crude and monitors only request.

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

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
dog: add 'node stat' command

$ dog node stat # show the stat once
$ dog node stat -w # watch the stat every one second

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