adding FloatOpt to the config parser

This patch just adds the ability to parse Float values from a config
using oslo.config.cfg FloatOpt class

Signed-off-by: AJ Ragusa <aragusa@grnoc.iu.edu>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
sw test tool: add a "note" for help to understand

Signed-off-by: TAKAHASHI Minoru <takahashi.minoru7@gmail.com>