register the config generator default hook with the right name

register the config generator default hook with the right name

No config generator hooks should ever be registered with a name that
belongs to another project. In this case, using oslo.middleware.cors
means that *every other project* that loads the middleware gets this
application's defaults when the generator is run on a system with
everything installed (such as a dev box with devstack). Use the name
of the app instead, to ensure that the defaults are only set when this
app's sample config and documentation are being generated.

Change-Id: I6a8c7d44b9db9325003ff2fdb667b0ced7739e96
Signed-off-by: Doug Hellmann <doug@doughellmann.com>