Smooth use of serial port for GRUB and/or kernel console

[nshalman]

Issue Description

It would be nice for people to be able to do initial setup of Mistify on machines with not graphical output using a serial port out of the box without any tweaking.

Acceptance Criteria (How do we know when this is done?)

Can boot up without VGA and see GRUB on the serial port and have the option to tell Linux to put console messages on the serial port and then have the console messages indeed come through on the serial port

See TritonDataCenter/smartos-live#379 for how SmartOS handles this