Also move component/stunnel to unstable

powerdns needs a pkgconfig file from lua to compile

nis module is linking against system libraries

This is almost the smae as for python3 (see e1cee1fc)

This reverts commit fb3ee44e
partially, for dream.

Add tests for Wendelin Learning Track tutorial
https://wendelin.nexedi.com/wendelin-Learning.Track

Add port-listening promises for all sources found in fluentd configuration file

There can be a short delay until the partially uploaded file is actually
removed, so wait a little bit before checking for its absence.

Our old subversion does not seem to support the expiration of letsencrypt root certificate, as we can see in [tests](
https://erp5js.nexedi.net/#/test_result_module/20210930-70CDB278/143): 

```
ClientError: ("Unable to connect to a repository at URL 'https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web'\nServer SSL certificate verification failed: certificate has expired", [("Unable to connect to a repository at URL 'https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web'", 230001), ('Server SSL certificate verification failed: certificate has expired', 230001)])
```

This is also what we observe when using svn command from ERP5 software release:

```
~/srv/slapos/shared/subversion/26833ca5dbfd6944dc2e584d0761dc89/bin/svn info https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web
Error validating server certificate for 'https://svn.erp5.org:443':
 - The certificate has expired.
Certificate information:
 - Hostname: svn.erp5.org
 - Valid: from Sep 26 05:47:35 2021 GMT until Dec 25 05:47:34 2021 GMT
 - Issuer: Let's Encrypt, US
 - Fingerprint: 01:98:FF:1B:68:A1:55:59:35:EE:1C:57:8A:6E:5A:22:1F:3E:B2:86
(R)eject, accept (t)emporarily or accept (p)ermanently? ^Csvn: E200015: Unable to connect to a repository at URL 'https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web'
```

Updating subversion and linking it with openssl 1.1 seem to solve the issue.

See merge request !1053

This has been superseeded by switch-softwaretype recipe.

See commit d9cbf829.

This is a follow up of 04938bff.

Nis module is linking against system library libnsl which is not slapos compatible.

Also note that we use printf instead of echo here because echo behaviour with \n is different with bash or dash.

openssh 7.7p1 has a compilation erro in Debian 11.

This reverts commit e5f9dee1,
now that slapos.recipe.build is fixed.

Allows to use recipe for cases when file is not present yet so it can return
some default (marker-like) value.