This driver is an oslo.config backend driver implemented with
Castellan. It extends oslo.config's capabilities by enabling it
to retrieve configuration values from a secret manager behind
Castellan.
Change-Id: Id7cf99bea5788e0a6309461a75eaa8d08d29641b
Signed-off-by: Moises Guimaraes de Medeiros <moguimar@redhat.com>