Rarely used https backend was missing the backend Via additions, thus it was
not transmitted there.

This reverts commit e7b48c0b.

This reverts commit 201d238a.

See merge request nexedi/slapos!1212

This is a fixup of bddc5491.

See merge request !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 !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.