Allow use of lowercase section names in conf files

Allow use of lowercase section names in conf files

Fixes bug #1189889

oslo.config-1.2.0 normalizes section names in config files to lowercase.
This means that simply by upgrading to oslo.config-1.2.0, users will now
be able to do e.g.

  [default_servicetype]
  description = ...
  service_definition = ...

Change the default config files to make it clear we recommend the use of
lowercase section names.

Note, the use of an alpha tarball of oslo.config requires pbr>=0.5.15
but we already require >=0.5.16.

DocImpact

Change-Id: Ia47fb3d168da71d3221b25979f8c9257d70dd64d