fix #4747: pass kernel cmdline parameters to target system

fix #4747: pass kernel cmdline parameters to target system

Parameters needed for booting during installation are best preserved
in the target cmdline as well - e.g. if you need a particular
cmdline switch for your system to boot at all - not having to add it
for the first boot of the installed system and manually adding it to
the bootloader config is an improvement.

This additionally enables us to drop the console parameter handling
for serial consoles (it is just one of the parameters to pass along).

Finally it fixes the regular expressions for the installer settings we
read from the cmdline (swapsize, maxroot,...) which were broken if
added as last entry.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>