Added option to run a script before chroot_script.

Signed-off-by: Vlad Ungureanu <vvu@vdev.ro>
how to use early_chroot_script

Signed-off-by: Vlad Ungureanu <vvu@vdev.ro>
Sample early_chroot_script

Signed-off-by: Vlad Ungureanu <vvu@vdev.ro>