[XENMON] Add argument check of "--ms_per_sample" option.

[XENMON] Add argument check of "--ms_per_sample" option.

If a value of "--ms_per_sample" option is larger than a value of
"--time" option, xenmon may generate no log file. So, too large
"--ms_per_sample" should be treated as an error.

e.g.
  % xenmon.py --ms_per_sample=2000 -t 1 -n
  usage: xenmon.py [options]

  xenmon.py: error: option --ms_per_sample: too large (> 1000 ms)

# Notice that a unit of "--time" is a second.

Signed-off-by: KUWAMURA Shin'ya <kuwa@jp.fujitsu.com>