dracut: install modules to /usr/lib

The dracut modules will be installed to /usr/lib64 while building 64bit
targets with multilib enabled, this causes runtime errors:

  dracut: Cannot find /usr/lib/dracut/dracut-functions.sh.
  dracut: Are you running from a git checkout?
  dracut: Try passing -l as an argument to /usr/bin/dracut

The dracut modules, 50-dracut.install and 51-dracut-rescue.install must
be installed to /usr/lib as Fedora 20 does.

Signed-off-by: Wenzong Fan <wenzong.fan@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>