fix(dracut): shellcheck regression in DRACUT_INSTALL calls

fix(dracut): shellcheck regression in DRACUT_INSTALL calls

If the DRACUT_INSTALL environment variable contains arguments (e.g.:
DRACUT_INSTALL="/usr/lib/dracut/dracut-install --debug"), its call cannot
be enclosed in double quotes. E.g.:

```
> export DRACUT_INSTALL="/usr/lib/dracut/dracut-install"
> "$DRACUT_INSTALL" > /dev/null
dracut-install: No SOURCE argument given
> export DRACUT_INSTALL="/usr/lib/dracut/dracut-install --debug"
> "$DRACUT_INSTALL" > /dev/null
-bash: /usr/lib/dracut/dracut-install --debug: No such file or directory
> $DRACUT_INSTALL > /dev/null
dracut-install: No SOURCE argument given

```