Our cinder.conf.sample lists all of the options that are defined by
drivers in the [DEFAULT] section. Since removal of single-backend config
(without enabled_backends) this is misleading as those options are
functional only when defined in [<backend_name>] section. This commit
aims to move all of the driver options to [backend_defaults] section.
Assumption is that this will affect only sample config generation and
should not break anything else.
Change-Id: Ia4766eb313e15adc92a92875519b22db64e95d65
1f62a411f4