Make the value and its changes easier to read.

Revert f8f72a17 ([erp5] don't use caucase generated certificate for now, 2019-03-12) since nothing prevents us drom using caucase certificate now.
 
Use [managed resources](slapos.core!259) to simplify existing tests and introduce tests for:

## Access Log

 - [x] balancer partition should produce logs in apache "combined" log format with microsecond timing of requests.
 - [x] these logs should be rotated daily
 - [x] an [apachedex](https://lab.nexedi.com/nexedi/apachedex) report is ran on these logs daily.

## Balancing

 - [x] requests are balanced to multiple backends using round-robin algorithm
 - [x] if backend is down it is excluded
 - [x] a "sticky cookie" is used so that clients are associated to the same backend
    - [x] the cookie is set by balancer
    - [x] when client comes with a cookie it "sticks" on the associated backend
    - [x] if "sticked" backend is down, another backend will be used

## Content-Encoding

 - [x] balancer encodes responses in gzip for some configured content types.

## HTTP

 - [x] Server uses HTTP/1.1 or more and keep connection with clients

## TLS (server certificate)

In this MR we also change apache to use a caucase managed certificate and add test coverage for:

 - [x] balancer listen on https with a certificate that can be verified using the CA from caucase.
 - [x] balancer uses the new certificate when its own certificate is renewed.

But we don't add support for:
 -  ~~balancer can be instantiated with a certificate and key passed as SlapOS request parameters (code [here](https://lab.nexedi.com/nexedi/slapos/blob/757c1a4ddee93659d5e2649e4252d87bf9494566/stack/erp5/instance-balancer.cfg.in#L208-213))~~ this use case is the job of caucase, so we no longer support this.

## TLS (client certificate)
 - [x] balancer verifies frontend certificates from frontend caucases ( also tested in "Forwarded-For" section )
 - [x] if frontend provided a verified certificate, balancer set `remote-user` header
 - [x] balancer updates CRL from caucases ( `caucase-updater-housekeeper` )
 - (NOT TESTED) balancer updates CA certificate from caucase ( `caucase-updater-housekeeper` ). Since this is would be complex to test and basic functionality of `caucase-updater-housekeeper` for frontend caucases is covered by CRL test, we don't test this for simplicity.

## "Forwarded-For" header

This was also covered by existing tests:  

 - [x] balancer set `X-Forwarded-For` header when frontend certificate can be verified
 - [x] balancer strips existing `X-Forwarded-For`

## Integration with the rest of ERP5 software release

This was also covered by existing tests:  

- [x] The https URL of each Zope family is published and replies properly
- [x] Some https URLs are generated for `runUnitTest`, so that test run with an https certificate. This is also covered by regular ERP5 functional tests.

See merge request !840

See merge request nexedi/slapos!839

https://github.com/eclipse-theia/theia/blob/v1.7.0/CHANGELOG.md#v170---29102020

Future Cython+ work will use it.

Fix for #20200514-218C705 - \[testnode\] frontend for log access

Depends on nexedi/erp5!1304

See merge request nexedi/slapos!848

This fixes the nextcloud SR, which was broken by
commit 92779bf4
(mariadb is not a part anymore).

This fixes commit a62e5e7b.
See also commit 491e6e28.

And set it as log_frontend_url in testnode config

Just add the following 2 lines in a SR:

[mariadb]
location = ${mariadb-10.4:location}

It does not build with GCC 8.2

Going Go1.14.9 -> Go1.14.10 brings in compiler and runtime fixes
including fix for crash in garbage-collector due to race condition:

https://github.com/golang/go/issues/40642
https://github.com/golang/go/issues/40641

Tested on helloworld SR.

See merge request nexedi/slapos!844

validators.url is enough, even for Caddy, to check that URL is correct, and
caddy_backend_url_validator was introduced before validators.

Also calling an external command for each slave takes a lot of time.

Thanks to this other sections can directly reference them, and so they are
correctly created as needed, so linking section does not need update-command

The password is anyway present in the section itself, so it's eventual change
will result with reinstalling the section.

Also change a bit existing frontend_url to manage it the same way.

This way buildout can reuse egg caches and it's a bit faster:

To run a simple instance buildout, from 2.837s it goes down to 1.875s.
To run slapos node instance 10 times just after requesting an ERP5 instance, it goes from ~112s to 98s

before:

    hyperfine "/srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U"
    Benchmark #1: /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U
      Time (mean ± σ):      2.837 s ±  0.275 s    [User: 2.481 s, System: 0.285 s]
      Range (min … max):    2.482 s …  3.222 s    10 runs

after:

    hyperfine "/srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U"
    Benchmark #1: /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/shared/python2.7/60364a13cc977dd5a894e0239ac889b9/bin/python2.7 /srv/slapgrid/slappart4/srv/slapos/inst/slappart0/tmp/soft/c63ba7265399450b28f9ea6d5667a5e7/bin/buildout -U
      Time (mean ± σ):      1.875 s ±  0.067 s    [User: 1.660 s, System: 0.148 s]
      Range (min … max):    1.816 s …  2.038 s    10 runs

See merge request nexedi/slapos!846

Changes configuration files to run repman tests in python3.

Adds the newly added to nexedi's repositories rubygemsrecipe (https://lab.nexedi.com/nexedi/rubygemsrecipe) to the list of tested eggs.

This also fixes rpath of rust binaries.

See merge request nexedi/slapos!845

Since 0.9.6 caucase stopped using the 128bits OID arc that caddy/golang does
not support, so nothing prevents us from using a caucase certiciate now.