[IMP] Allow to specify number of workers through environment variable

[zamberjo]

We are running a test that involves the generation of several reports.
The process would look something like:

    report_pdf = (
        self.env.ref("module.name_report")
        .with_context(force_report_rendering=True)
        ._render_qweb_pdf([obj.id])
    )

We set the force_report_rendering flag to not render in HTML since we want to check the PDF result but this process does not finish since the main process is blocked by the same execution.

Increasing the workers this does not happen. By default I have left it at 0 which is the default.

[sbidoul]

@zamberjo have you tried running your test in a HttpCase instead of TransactionCase?

[zamberjo]

Hi @sbidoul, I just tested it and using HttpCase it is no longer blocked, thank you. You can close the PR if you see that it does not contribute anything, even if it is for another case.

[sbidoul]

Thanks for the feedback!