Generate reproducible initramfs images

Generate reproducible initramfs images

With the same source of files, it should be possible to generate the
same image file with every dracut run.

To accomplish this, we modify the timestamps of the files we generate at
runtime, call gzip with "-n" and cpio with "--reproducible".

The cpio --reproducible option is not yet upstream though, so if you
feel like it should be then please nag at the cpio mailing list.
http://lists.gnu.org/archive/html/bug-cpio/2014-08/msg00000.html