proxmox-boot: read only first line of /etc/kernel/cmdline
following the commit of removing the wrong indentation of the linux
and initrd lines - this commit strips empty lines (and leading
trailing whitespace) in /etc/kernel/cmdline.
I managed to reproduce the issue reported in the forum [0] by adding
empty lines to /etc/kernel/cmdline) - without this - systemd-boot
booted quite happily even with the indentation.
considered using perl -pe with multiline matching but thanks to
Thomas' suggestion went with the shell-builtin read.
the check for existance of 'root=' in the resulting CMDLINE was added,
since my test-system had an empty line in the beginning, which again
rendered it unbootable.