Use new oslo.config api to generate configuration-group help

oslo.config recently updated its api to allow discovery of
help attached to configuration groups [1][2]. This patch
changes the list_opts function to use the new api and allow
for automatic generation of help on configuration groups.

[1] https://bugs.launchpad.net/oslo.config/+bug/1395819
[2] https://review.openstack.org/#/c/242472/

Depends-On: I3cbdaa7e5dfb75d4c9eb687e68d3a35e61550d1b
Change-Id: I8eabf52236bf571d42d3021f2485c1898cddd31a
1 file changed