Bluetooth: Mesh: Allow to be NODE when PROVISIONER is enabled

When PROVISIONER and CDB is enabled then IUT couldn't be a NODE.
This patch fixes this by not returning an error when CDB is not
configured. This is useful especially in testing environment, when all
the features are compiled in and we can choose role in runtime.

Signed-off-by: Michał Narajowski <michal.narajowski@codecoup.pl>