[fuel-ci] Separate VENVs for fuel-qa used in swarm jobs for 6.1, 7.0, 8.0 and master

[Vasyl Saienko]

At the moment all jobs use single VENV. It doesn't allow to install python dependencies with different versions for specific job.
This forces to update all code (for 6.1 and later releases) to support master libraries.
Jobs for specific release should be tied to own VENV.

[Denis Meltsaykin (dmeltsaykin)]

For Maintenance team this is a critical issue, we cannot release anything while Swarms are failing.

[Dmitry Kaigarodеsev (dkaiharodsev)]

Currently the issue solved by different slave labels on https://ci.fuel-infra.org/

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