Add the oslo.config entry point so that these options can be discovered
by oslo-config-generator. Add a simple tox env to generate a sample
config file with the available options. This file may be placed in
/etc/nova/conf.d to inject these options into the nova services.
Change-Id: I05b564418f3b9334e6a8033b52f165b8bab2eabf
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>