This reverts commit 1bd4fc32

Frontend can now do SSL client authentication to the backend. This is turned
off by default, but easy to enable by proper switch.

In order to achieve this result haproxy has been introduced as middleman just
before the backend. Also it came with rsyslogd, as haproxy can't log by
itself.

Documentation has been updated, also changelog has been introduced.

A lot of additional tests has been added due to adding additional component
(haproxy) which required a bit different ways to approach to the request input
data.

See merge request nexedi/slapos!771

Despite the new system does not support promise failing scenarios, use a
simple way to have such configurations in late way and massively test various
important cases for rejection, error reporting and similar.

By default do not offer authentication certificate, the switch
authenticate-to-backend can be used on cluster or slave level to control
this feature.

rsyslogd is used, as haproxy does not support writing log files by its own.

This is needed in order to provide future support for client certificates
to the backend.

Also it means that haproxy is used in all cases, with or without cache, and as
a result the "cached" version of caddy is dropped.

Let haproxy setup maxconn by itself, as it's wise enough.

Also trust that it'll detect and use proper limits, instead enforcing them in
the shell with ulimit trick (ulimit -n $(ulimit -Hn)).

As empty server alias can impact the configuration, add proper test for
checking it.

It's required to fetch all dependencies in all cases, as tarball preparation
can happen on machine, on which gcc would be used from OS, but in the end
package building can happen on machines without proper gcc.

In some environments it is required to have gcc provided by SlapOS, and simply
forcing seems better than setting bugs min_version.

the name of constructed records should be unique so use the slave
reference instead of the "origin" parameter to be sure it is unique.

Before this change, if 2 slaves have the same origin parameter
"foo.com", we have the following in zone-files.yml:

    [...]
    sa.continent.foo.com:
      - cname: cname.of.slave1.for.sa
    [...]
    sa.continent.foo.com:
      - cname: cname.of.slave2.for.sa

So only the cname for slave2 will be used.

Instead of passing various kedifa information to the profile generating
configuration use section kedifa-configuration and access later such grouped
values.

In context of frontend node reuse passed directory section to slave
configuration to improve readability and simplify future enhancements.

This reverts commit 92fd6909, which
incorrectly added test assertion files with 'test.test'.

Caddy's proxy stanza for defined path with spaces sometimes is working when
it's done like this:

  proxy /path with_spaces ip:port

It happens, that few first requests after starting Caddy it's working, but
then it fails with error message like:

  dial tcp: lookup with_spaces on ip: no such host

So to stabilise situation now paths are generated like:

  proxy "/path with_spaces" ip:port

ssl_proxy_ca_crt can be just empty value, and that's not acceptable.

Use @@LOCATION@@ template to provide proper prefix path.

These changes allow to build SlapOS on Debian Buster ppc64el.

The PowerPC 64-bits little endian platform appeared more recently into autoconf and therefore needed updated `config.sub` and `config.guess` files.

Somehow these only needed to be patched on autoconf itself which is quite dated (2012), and libyaml that does not ship it's own `config.sub` and `config.guess` files. Other components built fine out of the box.

`config.sub` and `config.guess` files were taken from Debian Buster itself. More information at: https://wiki.debian.org/AutoTools/autoconf

**This merge request would have to be backported to previous releases in the case components reference older releases of SlapOS, which, if I understand correctly, is the case some times.**

See merge request nexedi/slapos!780

autoconf and libyaml needed updated config.sub and config.guess files
on ppc64le.

gnu-config component was created to centralize updated config.sub and
config.guess files. autoconf and libyaml now extend gnu-config and
overwrite their bundled config.guess and config.sub with gnu-config's.

in the future, any component can extend gnu-config to update it's own
config.sub and config.guess files if necessary.

monitor app shows:

![monoring app showing /log url](/uploads/dbb22484f79ed1538a308c640d74c3dc/image.png)

but this URL can not be accessed:

![/log URL unauthorized](/uploads/cf74f2d8bb867123c39264d8f7d9de74/image.png)

The correct URL looks to be this:

![/share/private/log is OK](/uploads/4775d5d3841d8ffa68d67f2cf2b87b22/image.png)

See merge request nexedi/slapos!785

This MR includes the following steps:
1. Target Python 3
2. Upgrade powerdns from version 3.3.1 to version 4.2.1 --- which also means...
3. Rework the configuration to support the [new GeoIP backend config format](https://doc.powerdns.com/authoritative/backends/geoip.html)

See the commit messages for more detail.

Note: EDNS Client Subnet extension is enabled.

See merge request nexedi/slapos!764

With the recent powerdns upgrade, the GeoIP backend uses a new config
format, see zones-file.yml.jinja2.

zz.countries.nexedi.dk.rbldnsd (which maps IPs to countries) is replaced
by GeoLite2-Country.mmdb(1) (which maps IPs to countries & continents).

Note: zz.countries.nexedi.dk.rbldnsd is not deleted (yet?); it is parsed
to keep information about China and its IP ranges grouped by ISP.

cdn.conf.in (which maps RR(s) to countries) is dropped; it is replaced
by an equivalent mapping done inside zones-file.yml.jinja2.

Also, EDNS Client Subnet extension is enabled.

---
(1): Added in previous commit.

Note: Only boost>=1.35 and openssl are required to build powerdns from
source; ragel, bison and flex are also required if building from git.
See https://doc.powerdns.com/authoritative/appendices/compiling.html#dependencies

See merge request nexedi/slapos!781

Replace occurences of 2.7 version to:

 * just python part, in case if part was referred
 * to ${python:version} in case string was generated