The `interface_driver` option needs some clarification.
While we only support three interface mechanisms,
it's possible that deployers can use their own
interface driver, so using oslo_config's choices
for this option does not make sense.
Depends-On: I2c3d6e4234bf7185b8da3c8e1701069c3a165ffc
Change-Id: I1cc710dbe87e9e23fbed63dcd5f1017978393c66
(cherry picked from commit 26645f5db3)