[Fedora-livecd-list] Run livecd-iso-to-disk in the source environment with chroot

[Frederick Grose]

This version of livecd-iso-to-disk is reworked to use the source root
filesystem in a chroot by default, along with the livecd-iso-to-disk script
embedded in the source.  A --nochroot as well as a --avoidsourcescript
option are available for cases where the launching filesystem and/or
installation script is called for.

One can load a Live USB by these steps:
 1. mounting the source.iso
 2. determine its loop device, /dev/loopN
 3. call /mountpoint/LiveOS/livecd-iso-to-disk /dev/loopN /dev/target

All 3 steps could be avoided by providing some appropriate autorun scripts
for the iso, or including some standard install scripts that could be
invoked by clicking on them in Nautilus.

By mounting the source.iso LiveOS filesystem in a chroot enviroment, the
current version of software components, including the installation script,
on the source can be used for installation.  (If syslinux-extlinux is not
in the source, ext234,btrfs target devices will have to use the --nochroot
option and a system with the proper bootloader.)  An --avoidsourcescript
option is also added to allow installation with alternative scripts.

This new version of livecd-iso-to-disk prefers builtin functions, finds and
offers to unmount mounted targets, and reorders some compatibility checks
in order to bailout early, if needed.

If this passes further testing (the DVD and netinst installer paths are
untested), I can submit incremental patches for these changes.

Link to the reworked livecd-iso-to-disk script,
https://bugzilla.redhat.com/attachment.cgi?id=610112

Filed on this ticket,
https://bugzilla.redhat.com/show_bug.cgi?id=663986


Testing and comments would be appreciated.

            --Fred