While generating a sample config with "tox -egenconfig", some options
for the Nova, Cinder and Neutron client are not added to the [nova],
[cinder] and [neutron] section. I.e. "api_insecure" is not available for
all sections. Register the config options under the correct group while
generating the sample config.
Closes-Bug: #1613303
Change-Id: If54fd42f7a06c159bcb6df5f684dc1211a9b91e9
