Live configs: Make per-arch live configs

See merge request !9

This allows us to override all configs for a given arch.

For instance, ppc/ppc64 can use mesa-be versions of Mesa.

This removes the empty-password 'live' user from tarballs and Horizon
installation media.

We need to make this image fit on a 700 MB CD.

This feature requires Horizon 0.9.8 or newer; older versions will
silently ignore this as an unknown key (or fail in strict mode).

Ref: packages#206

This reduces the size of media significantly.

Configuration updates for BETA5

Closes packages#1114 and #385

See merge request !7

Ref: #388, #390

Closes: #385

This group is required for our disk mounting rules in user/udisks2.

Closes: packages#1114

Factor all of the repeated logic into a single 'live-base' script.

As used by 'automedia', directory permissions for '/root' were too
permissive. A change to this script and separately to 'automedia'
are required in order to have '/root' be 0700. To facilitate the
bind mounts for installing QEMU emulators for media creation, this
directory was inadvertently created with the wrong umask.

The '/usr', '/usr/sbin', and '/etc' directories were found to be
inconsistent with the output of 'hscript-image' for rootfs tarball
media, so the appropriate umask is now set.

A full audit for permissions should be performed.

This reverts commit 840e40c2.

Not needed as the rsync job has been resumed.

VERSION can now be overridden, and defaults to the current date in
%Y%m%d format instead of being hardcoded.

This drastically simplifies adding new DEs and removes a lot of
repetitive rules.

* Add XFCE and tarball configs for everything.

* Add firmware spins for aarch64 and armv7.

* Fix firmware installfile to make working discs.

The local script needs to run before it starts, so live configs need it
this way.  However, we don't want the tarballs to have it there.

This ensures our local script that sets the time can run *before* the
daemon starts.  Once the daemon has started, it is no longer possible to
set the time manually using chrony.

Ref: #361

Put the graphical runtime in its own runlevel so it can be chosen or not
chosen by the user during startup.

Ref: horizon#346

This depends on the new livecd-support-xfce package.  I've only tested
this config on ppc64 but I have no reason to believe it wouldn't work on
other architectures.

configs/horizon/ scripts for XFCE media will come after beta5 release.

This requires Horizon 0.9.8pre3 or later (horizon@615278f3).

This allows the user to have network access without poking at it, in
most scenarios.

Ref: horizon#361

Ref: horizon#361

This allows Horizon's "Select Installation Disk" page to retrieve disk
sizes properly.

Still WIP, but seem to be working so far.

This tool is "deprecated" anyway, and we need usable media.