fix DRACUTDIR to be in /usr/lib/dracut

Unforunately the dracut module doesn't work if installed in
/usr/local/lib/dracut.  It must always be installed in
/usr/lib/dracut regardless of the install prefix.
Merge pull request #121 from jpoimboe/dracutdir

fix DRACUTDIR to be in /usr/lib/dracut