[vagrant] do not set the serial console in miniOS, so that the interactive...

[vagrant] do not set the serial console in miniOS, so that the interactive console goes to the vagrant screen

Useful for instance if enabling an initramfs breakpoint (e.g. add
`break=premount` in the kernel cmdline)

Another option is to enable kaconsole in the vagrant env, e.g. by
configuring nodes to expose the virtual serial ports on TCP ports
(supported by virtualbox) than configuring the cluster to use them with
netcat.