This is a fixup of bddc5491.

See merge request nexedi/slapos!1188

Now, with the `chain` option, you can source a chain of activate script
created by the macro.

In addition, the `deactivate` function will return to the initial environment.

The `message` option allows to write a message that will be displayed when sourcing the script.

The `environment` option allows you to write your own environment variables for the virtual environment.
To use it:
environment =
  <env-name> = <env-value>

See merge request nexedi/slapos!1211

MarkupSafe 1.0 is not compatible with Python 3.8

See merge request nexedi/slapos!1208

Add open62541 library compilation as beremiz's runtime includes a CLI PLC project compiler which needs this library.

Run wait_for_activities macro in selenium test on erp5 with activity subscribed may end with:

INFO SQLBase Got a lock error, retrying...
.....
WARNING waitress.queue Task queue depth is 1
WARNING waitress.queue Task queue depth is XXX
....
503 Service Unavailable

curl invocation was incorrect, and was working only in some conditions by
chance, so fix it fully. Now the test fails in all conditions correctly,
including sanity assertion.

Profiles and required scripts are converted to be python3 only compatible.

Started with 2to3, then added some manual changes.
Improved result configuration with returning incorrect configuration.

In the end curl seems the tool which gives full control over order of the
cookies, especially with upcoming migration to python3.

Due to python2 dict handling the problem has been hidden, but smart order
of disabled-cookie-list setup exposed the problem.

Fixes problem described in https://bugzilla.redhat.com/show_bug.cgi?id=2079938

Support absolute and relative paths. Paths starting with "rbd:" are special,
and they point to the rbd endpoint, served by Ceph.

cache parameter is optional, in case if present, will be used as-is, even with
empty cache.

external-disk-number, external-disk-size and external-disk-format has been
removed from the schema to become hidden, nevertheless it's expected to be
fully supported, as long tests are kept.

Loudly fail in case if old and new ways are used in the same time.

Switch to pure meson build system and adapt configuration for SlapOS
requirements.

Support multiarch env by simply linking from lib64.

Version 249.6 incorporates fix from https://bugs.gentoo.org/824026 for:
  meson.build: ERROR: Object <[BooleanHolder] holds [bool]: False> of
  type bool does not support the +