Wait to trigger udev until multipath settles

See:
http://git.kernel.org/cgit/boot/dracut/dracut.git/commit/?id=d829e7fce273e9dbd8a71dbf71612556331f28fa

Change-Id: I71dc86c7831b5e31b8d3b89d6a014bbd0ccc57a1
Signed-off-by: Ryan Barry <rbarry@redhat.com>
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>