Fix IPMI console config to work with our HW

The IPMI console on most of our currently deployed systems is wired to ttyS1,
while on other systems its ttyS2. Move this into a configuration
parameter `common.ipmi.serial_console`.

Update check-kernel-options to accept a console on either port and fix
double negative in warning message.

Configure primary kernel console on virtual tty 1, rather than 0 so
we can switch back to it and login prompt appears after boot as
expected.

Move update-grub into a handler