[PATCH 33/50] We now have a simple hook structure and 3 defined hook points.

[PATCH 33/50] We now have a simple hook structure and 3 defined hook points.

Any script placed in /pre-udev will be sourced just before udev starts
device scanning and loading.

Any script placed in /pre-mount will be sourced just before we try to
mount a root filesystem.

Any script placed in /pre-pivot will be sourced just before we switch to the
new root filesystem.

These hooks should be the minimum needed to add back plymouth and deal with
more advanced filesysem mounting needs (multipath, iscsi, nfs, nbd, etc.)