We can have an uppercase member interface in the bridge config

bridge br1 {
    enable-vlan
    member {
        interface Vxlan1 {
        }
    }
}

But an upper case VXLAN interface can not be created.

During debugging of this I also noticed that there are multiple different calls to confi.exists() in vyos.configdict - some use string, some use list as argument.
This has been streamlined to only make use of lists.