On backend side headers are asserted in tests:

 * X-Forwarded-For
 * X-Forwarded-Proto
 * X-Forwarded-Port
 * Host

In order to pass cleanly X-Forwarded-For from the frontend to the backend,
it's passed as X-Forwarded-For-Real in case of cached slaves.

Noted problem with IPv6 endpoint was used, as in this case 6tunnel IP would
be used.

QUIC is not used at all, and became superseded by HTTP/3

Customized configuration support is not used since introduction of
Caddy software, so there is no need to support it anymore.

also add CPU=native for possibly better performance.

See merge request nexedi/slapos!769

so that we can create caucase-updater for fetching CA / CRL only purpose.

To avoid

[2020-06-03 15:35:15,590] INFO     While:
[2020-06-03 15:35:15,590] INFO       Installing.
[2020-06-03 15:35:15,590] INFO       Getting section template-cloudooo.
[2020-06-03 15:35:15,590] INFO       Initializing section
template-cloudooo.
[2020-06-03 15:35:15,591] INFO       Getting section
dynamic-template-cloudooo-instance-parameter-dict.
[2020-06-03 15:35:15,591] INFO       Initializing section
dynamic-template-cloudooo-instance-parameter-dict.
[2020-06-03 15:35:15,591] INFO       Getting option
dynamic-template-cloudooo-instance-parameter-dict:gcc.
[2020-06-03 15:35:15,591] INFO     Error: Referenced option does not
exist: gcc location

On debian 8.5 cloudooo refuses to start with:

    ./parts/libreoffice-bin/program/soffice.bin: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.9' not found (required by ../parts/mesa/lib/libGL.so.1)

some more info:

    # dpkg  -S  /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.20
    libstdc++6:amd64: /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.20

Create a Software Release for Replication Manager 2.1

https://github.com/signal18/replication-manager

See merge request nexedi/slapos!719