Use the same paths in dracut.sh as those set with configure script

Makefile alters destination main dracut script and sets dracutbasedir to
the value of pkglibdir set in configure.
Install dracut-install into libexec dir instead of lib dir

dracut-install script is the only thing ABI specific atm.

See https://bugs.gentoo.org/show_bug.cgi?id=485218 for details on the
problem.