Add oslo.config.opts entry_points in setup.cfg

oslo-config-generator relies on these entry_points listed
in setup.cfg to add options to the generated sample conf
files in different projects. So we should expose options
in oslo.log.

Closes-Bug: #1391742
Change-Id: I7c339484f17c4067ad7c82eb7f7208ef6d8be417
Merge "Add oslo.config.opts entry_points in setup.cfg"