`enable_authentication` parameter of `backend-list`
was not documented.

This release should be now stable enough for release

/reviewed-on nexedi/slapos!391

It is combination of requestoptional and serialised.

In order to avoid needless inheritance create JSONCodec and use it, also
with renaming Serialised to RequestJSONEncoded.

Also provide a test asserting that important log is seen in case if no expected
return is set.

Add testfixtures module to catch logging.

if saucelabs_dict is present, then generate delegate runTestSuite to launch test with saucelab
else default one is created

  it  clean up....

  Up to some extent we would like to set diskcache=none and diskaio=native

This reverts commit 2c79bee1 because it depends on rdiff-backup version 1.3.4nxd4 which is not stable yet.

This reverts commit 9b3dfa01

On runner importer script, when updating database, set timeout to 5 seconds (same value as the default in python sqlite3 module: https://docs.python.org/2.7/library/sqlite3.html#sqlite3.connect). If database is locked by another process we wait a bit instead of raise immediately "database is locked". Importer script will raise if database is locked for more than 5 seconds.

/reviewed-on nexedi/slapos!384

they are already pinned in stack/slapos.cfg

When slapos.libnetworkcache is not installed, then shacache is not
enabled, so SR will no longer build when there's a dead link.

/reviewed on nexedi/slapos!379

See https://www.erp5.com/group_section/forum/No-test-results-rtSJ3H4fpC

/reviewed-on nexedi/slapos!382

https://github.com/v8/v8/wiki/Building%20with%20Gyp

aspell-en-dictionary, groonga-normalizer-mysql, file-msooxml, apache-antiloris are not shareable, they write files in other parts.

With new rdiff-backup version, it is possible to speed up push process by ignoring UID/GID changes (as it will always be different because of different partitions)

/reviewed-on nexedi/slapos!378

stack/slapos.cfg: Add slapos.extension.shared. This extension creates .shared file in software directory as a mark of software that was built with shared feature.

This usage of textwrap.dedent *sometimes* does not work and sometimes
create files with indentation, so we don't have "#!/bin/sh" as first
line but "    #!/bin/sh"

Use a "safer" version that should work in all cases.

perl path does not need extra /bin

See nexedi/jio@4b8bddba

Rework perl installation to install each package in a separate directory.

Each package install a `perl` interpreter for each package, which is implemented a shell wrapper setting `$PERL5LIB` with the path of this package and its dependencies.

To install a perl package, use `perl-CPAN-package` macro, like in this example for a fictional `XXX::YYY` package:

```
[perl-XXX-YYY]
<= perl-CPAN-package
module = XXX/XXX-YYY
version = 1.2.3
md5sum = ab68b329da9893e34099c7d8ad5cb9c940cd123
```

This will download package from https://www.cpan.org/modules/by-module/XXX/XXX-YYY-1.2.3.tar.gz and install using the usual `perl Makefile.PL && make && make install` sequence.

To install package with dependencies, use the `inc=` argument, like in this example for  another fictional package `XXX::ZZZ` package that would depend on `XXX::YYY` and `XXX::ABC` :

```
[perl-XXX-ZZZ]
<= perl-CPAN-package
module = XXX/XXX-ZZZ
version = 1.2.3
md5sum = 401b30e3b8b5d629635a5c613cdb7919

inc = ${perl-XXX-YYY:site_perl}:${perl-XXX-ABC:site_perl}
```

The full list of options is described in the [macro](https://lab.nexedi.com/nexedi/slapos/blob/a5bec95c/component/perl/buildout.cfg#L31-65).


That macro creates an interpreter for each package, but sometimes we need to create an interpreter with multiple packages. The `perl-wrapper` macro is available for this. It also accepts a `inc=` argument in the same format. Because this wrapper is implemented using `-I` argument, it is also suitable for scrips running in perl [taint mode](https://perldoc.perl.org/perlsec.html#Taint-mode-and-%40INC), like the w3-validator we are using.

All perl components and perl usages have been updated to this new infrastructure.

Some (apparently) unmaintained components were using an obsolete `slapos.recipe.build:cpan` recipe. They were used only in mioga2 from unstable, so I moved them inline in mioga2 software.

/reviewed-on nexedi/slapos!341