- fix VM_SAVE_TARBALL parameter support
- grub: save ang read default menu item (thanks jqt4@, sin@)

1. Didn't work before because the variable was not exported.
2. Fixed the logic broken by the introduction of support for saving
the selected item on the FAT partition.

The code is given in accordance with the documentation
See-also: commit 2987fa8f

If the ISO image has a FAT partition and the image is written
to a flash drive, then it is possible to write to this partition
of the flash drive.
This is necessary, for example, if the user
does not want to install the system, but wants to constantly work
in LiveCD mode with or without recording sessions.
In order for this code to work, you need to make changes
to the FAT partition of the image on the flash drive:
Add the 1st line to the grub.cfg file:
set pfxfat=${prefix}
Write a 1kb file grubenv.
If grub.cfg contains a line like '^default=id',
then the read value is not used.

This prepares the ability to write and read
the default menu item from the grubenv file.
If grub.cfg contains a line like '^default=id',
then the read value is not used.
Setting the default menu item from the grubenv file
will be indented inside the 'if' optator and therefore
does not match the '^default' pattern.

- build-vm: Add ability to build .img.xz (thanks sem@)
- reports.mk: optimiztion for generate rpm and srpms lists (thanks mike@)
- reports.mk: generate targets.svgz instead targets.png
- add VM_SAVE_TARBALL parameter
- add MKIMAGE_PREFIX parameter
- kernel: optimization use/kernel/initrd-setup
- set STAGE1_INITRD_BOOTARGS in initrd-propagator
- slinux 9.1
- education 9.2

It is necessary to monitor the state of syslinux in Sisyphus.

education: use use/power/acpi instead of +power because this leads to a forced shutdown [distrtest-3933]

Previously, you had to specify two parameters MKIMAGE_PREFIX and
GLOBAL_PREFIX with the same value - the path to mkimage. And this
behavior has not been documented. The GLOBAL_PREFIX variable is
defined in mkimage in config.mk and rules.mk.

rtc not needed in initrd.

Not needed more. uuid assigned directly in configs.

make-initrd supports adding module directories.

Since we are now using fuuid, it doesn't depend on mkimage version.
But it depends on the propagator version.
Needed propagator >= 20210329-alt1
See-also: commit 52e90c26

beremiz removed from Sisyphus.
See-also: http://git.altlinux.org/tasks/archive/done/_265/271405

As new exfat filesystem is merged into linux-5.7 kernel, exfatprogs is
created as an official userspace utilities that contain all of the standard
utilities for creating and fixing and debugging exfat filesystem in linux
system.
std-def kernel in Sisyphus 5.10.

The parameter is used to save the intermediate tarball used to
build the virtual machine image.

SVGZ is more than a hundred times smaller than PNG.
a