Since different distros may or may not use vol_id in udev, and blkid
is generally replacing vol_id, abstract them out into a function which
tries to use vol_id first and blkid second, on the assumption that
blkid can take over for vol_id if vol_id is no longer there.
This also eliminates --skip-missing. Check scripts should now check
to ensure that any files and settings they will copy from the host
system actually exist when called without arguments.
The check scripts are also updated to not try to source dracut-functions
which(1) is a perfectly good way of checking if a command is on the path.
Victor Lowther