First of all , the 'jethro' based images are quite old by now, we have had support for krogoth and morty since that. Unless if you have a specific reason to use jethro, i would recommend to switch to 'morty' now.
All our images have the OE 'debug-tweaks' feature enabled, so you should be able to login as root without any password with any of the default RPB images. I think we need to understand why you can't build the rpb-console-image instead. Do you have any logs? Or maybe the 'jethro' builds is broken..