So far kiwi used a static serial line setup of the console
type was configured to use a serial console. However if
different parameters are needed there was no way to change
the static setup. This commit adds a new bootloader attribute
called serial_line which allows to specify the serial line
parameters for the grub bootloader e.g
serial_line="serial --speed=9600 --unit=0 --word=8 --parity=no --stop=1"
Please note serial_line takes the value as it is given and
adds this as a line to the grub configuration or as content
to the variable GRUB_SERIAL_COMMAND. No further validation
of the information takes place by kiwi. This Fixes#1401
Grub supports a style setting that influences the display of
the menu depending on the configured timeout value. With this
patch kiwi allows to specify the style via a new bootloader
parameter named timeout_style="hidden|countdown". If not set
the grub default applies which shows the menu in any case.
This Fixes bsc#1165730 and Fixes#1404
