Bluetooth: Mesh: Refactoring provisioning to make all OOB auth working

The current implementation has hidden dependencies that break
OOB authentication if provisioner does not have the configured
input or output fields used for device capabilities.
It didn't allow to pass several OOB authentication cases.
After refactoring provisioner behavior is independent to
provisionee settings.

Signed-off-by: Aleksandr Khromykh <aleksandr.khromykh@nordicsemi.no>