Fix "--debug" parameter for dracut

Fix "--debug" parameter for dracut

remove "-d" as a short-alias for --debug. It collides with the
--driver short-alias.

If --debug is set, inst_script() spews binary "garbage" to the screen
which are interpreted as control characters by the terminal, prompting
the user to call "reset" after dracut has finished. This is related to
set -x  printing binary headers from files to stdout.
As inst_script() is only checking if it is a script it should copy by
reading the first 80chars of the file and checking for the shebang line,
it is safe to call tr on the read in data and remove all unprintable
chars if the debug switch is set.