Comment 8 for bug 1799161

Reproducer: https://pastebin.canonical.com/p/YVdYQr3tDg/ (after this command set execution node is not able to deploy; error like in bug description is shown; also "maas %user% bcaches read %node_id% throws the same exception)

Valid configuration (succeded only after deleting bcaches manually via GUI): https://pastebin.canonical.com/p/w8F475Mn5F/