use perl instead of (g)awk to clean /proc/cmdline

use perl instead of (g)awk to clean /proc/cmdline

this awk line only works with gawk because of implementation differences
between awk alternatives.
debian has mawk installed by default, and mawk does not implement word
boundary regex. to avoid having to depend on gawk, we can just use perl
instead.

Signed-off-by: Oguz Bektas <o.bektas@proxmox.com>